Indulge yourself in a tiny bit of time travel here and check out this video, a condensed version of Costolo’s interview with Ad Age editor Abbey Klaassen from last week. This was when Costolo was still technically COO, and not CEO, but that’s not relevant here. The clip is well worth watching if you want to get a good sense of where Twitter thinks it’s at when it comes to ads.

And it gives you a good sense of where Twitter think it’s going, period. Check out the comps that Costolo throws out when he talks about his company: YouTube, Google (GOOG), Facebook. That makes plenty of sense–that’s why investors have put a $1 billion value on the company–but it also shows you how far the company has to go.

This time around, the CEO of the world’s biggest social network is making his case to advertisers at the annual advertising schmoozefest in Cannes. He’s scheduled to take the stage Wednesday afternoon, and his interviewer will be Advertising Age Editor Abbey Klaassen.

After Zuckerberg’s appearance at D8, I heard lots of chatter that he would have to stop taking questions in public. But unless the 26-year-old plans to stop running the company he founded, there’s no way that can happen. So best to get right back on the horse/bicycle/insert-your-own-metaphor here.

The good news for Zuckerberg: Facebook’s privacy issues don’t seem to have diminished advertisers’ interest in his site. Even better: After he makes his presentation, responsibility for the real pitching goes back to his large, expensive and top-shelf ad team, which has already helped the company rake in a lot of ad money.

Then again, they still have plenty of work to do. Financial Times:

Just two years after beginning to monetise its audience in earnest, Facebook’s revenue per user is already half the level of that achieved by portals such as MSN and Yahoo, Mr. Maude says. But relative to the many hours most users spend on Facebook each month, its income is “way behind” that of those more established sites.

Richard Pinder, chief operating officer of Publicis Worldwide, says Mr. Zuckerberg should keep his pitch to Cannes attendees simple.

“Most of the people making the big decisions [in ad spending] are not on Facebook,” he says. “They fear Facebook. Zuckerberg should explain what it is and why it works, and not make them feel bad about it.”