For context: In Silicon Valley, you often find fabulously wealthy people going back to the drawing board — hoping for another strike of genius so they can prove they’re good instead of lucky. So-called “serial entrepreneurs” are an exalted local species, and everyone wants to be one.

Here are some of the latest efforts on that front, all of whom seem worth keeping an eye on:

1. Yelp co-founder Russel Simmons, who left the local reviews giant a year and a half ago, is working on an education project called Learnirvana.

It looks like Learnirvana’s first product, Lentil, just came out. It’s a Web tutor program that helps users learn the capital cities of the world or to read Japanese through constant quizzing. The interface is simple and unassuming, and had me recognizing some basic kanji within a few minutes.

A source said Simmons has been dreaming up this kind of product since before Yelp started. Simmons did not respond to requests for comment.

Yelp filed to go public last month.

2. YouTube co-founder Jawed Karim, who left the company in its early days to finish grad school (but still made tens of millions of dollars when it sold to Google), has created a travel photography site called Fotons.

Fotons’ “about” page says: “Our mission is to create the best collection of great photos from around the world. With your help we aim to catalogue every notable country, city, building, river, stadium, statue, castle, library, zoo, island, river, cave, volcano — you name it.”

Users are told that they can only upload photos they have taken themselves, and that each picture must be at least 1,600 pixels wide or tall.

Karim said over email that Fotons “is in the middle of some big changes.” In other words, he warned not to look at the current site as a fully baked product. But that doesn’t mean it’s not usable now.

(It should also be noted that both Simmons and Karim worked at PayPal in the early days, and as such are part of the “PayPal Mafia.”)

3. Lastly, and perhaps the most vaguely, 23andMe co-founder Linda Avey — who left in 2009 to start a foundation focused on Alzheimer’s research — has a new company called Curious.

Curious has a only landing page for now, but a source said the company is working on topics around monitoring and sharing personal health information. Avey did not respond to a request for information.

Based on public posts, it seems Curious has three co-founders: Avey; Mitsu Hadeishi, who was previously at DonorsChoose.org; and early blogger Heather Anne Halpert.

This year’s commemoration is more muted. Basically, just a blog post that notes that the site is really, really big.

How big, you ask?

• YouTube users are now uploading 48 hours of video a minute. That’s up 37 percent in the last six months, and 100 percent in the last year. YouTube says the increase comes in part because it’s easier than ever to upload stuff, and in part because YouTube has started embracing lengthy live streaming sessions.
• YouTube users are now watching more than 3 billion videos a day. That’s up 50 percent from the last year, which is also a huge leap, though the growth rate has declined a bit: Last year, views doubled from a billion a day to two billion in six months.

But if you really want context for YouTube’s growth, go back and check out what it was doing in its first year: In December 2005–when Lazy Sunday first hit, and the site had become a mainstream success–viewers were watching 2.5 million videos a month.

And since we’re going back in time, here are three historically important YouTube videos:

Here’s the first clip ever uploaded to the site, back in April 2005, from little-known co-founder Jared Karim:

And here’s the clip uploaded by Steve Chen and Chad Hurley in October 2006, announcing that they’d sold the site to Google:

And here’s Tillman the dog, a 2007 video that showed up in Apple’s early iPhone commercials, and ended up becoming shorthand for the site’s user generated content.

Etacts, which participated in the Y Combinator program earlier this year, offered a free Web app and plug-ins that helped Gmail and IMAP users manage their email relationships by showing information about their contacts’ social Web activity and communication history.

The start-up, co-founded by recent Duke grads Howie Liu and Evan Beard, had raised $650,000 in funding from Ron Conway of SV Angels, Eric Hahn of Inventures Group, Jim Young from Hot or Not, Lorenzo Thione and Barney Pell from Powerset, Joshua Schachter from Delicious, and YouTube co-founder Jawed Karim. And I believe Ashton Kutcher was involved as well.

Etacts will no longer accept user sign-ups as of today and will delete all user data effective January 31, it said in an email sent to users.

Etacts’s product was quite similar to that of another Y Combinator company, Rapportive. Salesforce also just bought another YC company this month, Heroku, for $212 million in cash.

The move will be a formal acknowledgment of a practical reality: The video site is already under the day-to-day control of Google veteran Salar Kamangar, and industry insiders have been speculating that Hurley would step out for more than a year. Hurley himself told TechCrunch’s Robin Wauters that he’s been a de facto advisor for the past two years.

Hurley’s departure means that all three of YouTube’s co-founders have moved on. Jawed Karim had left the company before Google acquired it for $1.65 billion in 2006, and Steve Chen left his spot as chief technology officer in the fall of 2008. No word on what Hurley’s next full-time gig will be.

UPDATE: Hurley’s official statement, released via Google tonight, reiterates what he’s already said onstage–”For the past two years, I’ve taken on more of an advisory role at YouTube as Salar Kamangar has led the company’s day-to-day operations. I will continue to serve in an advisory capacity and am excited to witness the next phase of YouTube’s growth.”

Here’s Hurley and Chen in what still may be my favorite YouTube video, shot shortly after they sold their start-up:

Because if you’re trying to handicap the way the copyright lawsuit pans out, today’s document dump won’t do much to help you. There are revelations here, but they’re of the minor and historical variety, and I’ll get to some of them later.

No smoking gun, though. Just a lot of chest-beating and desk-thumping as both sides talk past each other.

Still, it does make for fun reading if you’re of a certain troubled mindset. If you’re not, here’s a summary:

Viacom’s case: YouTube was full of content that wasn’t supposed to be there, and both YouTube and Google knew it.

Of course they knew it! Anyone who visited the site in 2005 and 2006 knew it. The problem was what to do about it.

And that’s the most interesting part of the emails and IM exchanges Viacom has dug up: They let you watch YouTube’s co-founders, and later, Google executives, argue over the best way to keep the site growing like a weed while fending off the lawyers.

Actually, they knew the lawyers would show up eventually. “Ok man, save your meal money for some lawsuits! ;) no really, I guess we’ll just see what happens,” co-founder Chad Hurley tells partners Steve Chen and Jawed Karim via email in July 2005, as the three men decide to leave some copyrighted stuff on the site.

As as YouTube boomed, Google (GOOG) was trying to figure out how its lackluster Google Video site could compete. The big debate, according to former executive David Eun: “Whether we should relax enforcement of our copyright policies in an effort to stimulate traffic growth, despite the inevitable damage it would cause to relationships with content owners.”

Google’s eventual answer, of course, was to buy YouTube. But it went in with open eyes. A due diligence report estimated that just 10 percent of the “premium” stuff on the site was authorized.

Google’s case: Viacom–which talked about buying YouTube–was perfectly happy to use our site to market its movies and TV shows. Until it wasn’t.

Of course it was! In 2005 and 2006, all of the entertainment companies were desperately trying to get their clips in front of the site’s huge audience. Even more so at Viacom (VIA), whose youthful audience was spending lots of time on YouTube.

And the fact that Viacom executives, who had lost MySpace to Rupert Murdoch (remember when MySpace was a world-beater?), were thinking about buying YouTube–in part so Murdoch wouldn’t get it–shouldn’t be surprising, either.

Google makes a lot of the fact that Viacom “secretly” uploaded videos to YouTube, either via its employees or from marketing shops it hired. But I don’t get the impression that the “secret” uploads were supposed to dupe YouTube. I get the impression they were trying to dupe YouTube users into thinking the videos were edgy and cool.

“The goal is to make it look “hijacked,” an executive at Viacom’s Spike network told the producers of a mixed martial arts show, describing a video he gave them so that they could seed it on YouTube. The idea was to make the clip “look as though it was leaked out by production.”

Viacom’s embrace of YouTube does bolster Google’s case in one way. Google shows, fairly effectively, that Viacom’s lawyers have had a hard time figuring out which YouTube clips the company authorized. If Viacom can’t figure out what’s supposed to be on the site, Google argues, how do you expect YouTube employees to know?

So. Strip out all of the depositions, documents and emails, and we’re back to where we started. This case will hinge on the way the court decides to interpret federal copyright law.

Viacom argues that YouTube is a video version of Napster or Grokster–designed to profit from intellectual property it knows is stolen. And Google argues that it’s doing exactly what the Digital Millennium Copyright Act tells it do–asking its users to behave, hoping they do, and taking down offending clips when their owners ask them to.

So pay attention to that ruling–it’s going to be really important. But unless you’re paid to keep an eye on digital media, you can ignore most of today’s paperwork.

[Image credit: Michele Hubacek]

• $516 million to Sequoia Capital, which invested $9 million in the company
• $334 million to co-founder Chad Hurley
• $301 million to co-founder Steve Chen
• $85 million to Artis Capital, which invested $3 million
• $66 million to co-founder Jawed Karim

These numbers are all from documents filed by Viacom (VIA); they also indicate that five other YouTube employees received shares worth a total of $33.4 million.

Bear in mind that these numbers are based on the closing price of Google’s stock on Nov. 13, 2006. Google (GOOG) shares have bounced around dramatically since then, so the actual value of the payout could vary quite a bit depending on when–or whether–recipients sold their shares.

Why is any of this relevant to the case? Viacom’s suggestion is that YouTube’s employees and investors were focused on a big payout and wanted to build the company quickly–and that they were willing to accept copyright violations if that helped them achieve their goal. Again, not sure if this will matter in the court’s eyes.

This is old news, literally: Chen left his spot as chief technology officer last fall, though he remains employed at Google (GOOG), which bought his company for $1.65 billion in 2006. “Steve shifted his focus to help with some Google engineering projects. He’s still involved with YouTube and invested in its success,” says YouTube spokesman Ricardo Reyes via email.

Google hasn’t officially named a replacement chief technology officer for Chen, and people at the company say the job no longer exists. But the highest ranking engineer at the company is now Louis Perrochon, who has been at Google since 2003.

Chad Hurley, who co-founded YouTube with Chen and Jawed Karim in 2004, remains the company’s CEO. But it’s not unusual for founders to move on from their companies within a few years of selling them.

The fact that Chen’s move  has gone unreported until now should underscore that his departure didn’t represent a major org chart reshuffling. The technical challenges of the site have long been handled by a large engineering team, which makes sense considering that the challenges themselves are large. YouTube now uploads 20 hours of video per minute.

Chen was reportedly working on a technology incubator project last fall along with BitTorrent co-founder Ashwin Navin; no word on what Chen is actually doing at Google now.

Here are Chen and Hurley in a video they shot and uploaded on Oct. 9, 2006, the day they sold their company to Google.