Blippy, a start-up that lets users broadcast their credit card transactions online, will open itself up to the public today and announce a slate of high-profile Silicon Valley investors.

The size of the investment–$1.6 million–is actually not so large as the names on its funding roster.

They include: Sequoia Capital, Charles River Ventures, well-known angel investor Ron Conway, Twitter CEO and co-founder Evan Williams, and a trio of splashy entrepreneurs: Jason Calacanis, James Hong and Ariel Poler.

They are all presumably hoping the site–with the unlikely name of Blippy and headed by longtime Silicon Valley entrepreneur Philip “Pud” Kaplan–will become a viral hit with users and yet another step in the continuing socialization of everything a person does online.

The San Francisco-based company, which has only four employees (including Kaplan, who has also put his own money into the venture), has been in invitation-only private beta for the last several months.

In an interview last night, Kaplan said that the site now has about 5,000 users, accounting for $5 million in purchases in just the past few weeks. An average transaction, according to Blippy statistics, is just above $42.

Kaplan said he hoped Blippy would soon log $1 million in transactions per day.

“We are hoping to create a site that is useful and informative to people, based on a Twitter model of sharing information in an open way,” said Kaplan. “People care about what they spend and we think this is an obvious thing to share.”

Indeed, Blippy takes online transparency even further, allowing a user to automatically post on its Web site messages about the type and amount of the transaction every time they use a credit card–at least the one they designate as their “Blippy” card–for others to see and comment on.

The twist of Blippy–whose motto is: “What are your friends buying?”–is that it is more passive than the more active tweeting or texting.

While most of the transactions don’t contain a lot of information–for example, “cat spent $3.55 at In-N-Out Burger”–Blippy is obviously going for deeper information, which it already collects for sites like Apple (AAPL) iTunes and Amazon (AMZN).

Retailers, restaurants and other vendors might also benefit from the flow of information, finally learning who their best customers really are and perhaps rewarding them.

And, of course, the key part is that your friends see what you are buying and you can all jabber (or gripe) online about what you bought, how much you paid and what you thought of the purchases.

How all this will make money is still being pondered, of course, but one might imagine a dedicated Blippy credit card or some kind of innovative analysis of the spending data or even group-sale offers to users.

And integration with Facebook and Twitter seems inevitable, eventually widening the circle of nosy friends, as does the emergence of reviews, mobile apps, search and more.

Kaplan is best known for a site he created during the Web 1.0 bubble, FuckedCompany, which chronicled the ongoing start-up implosion as it happened.

He later started online advertising service AdBrite, followed by a short stint as Entrepreneur-in-Residence at Charles River Ventures.

It was there that he met Blippy co-founders Ashvin Kumar and Chris Estreich.

Kaplan said the money raised was enough to fund Blippy for the next 12 to 18 months.

But why not hear him talk about Blippy? Here is the video of a BoomTown interview with Kaplan, which I posted in late December: