When Jimmy Fallon took over the Late Night franchise, he inherited comedy's highest-profile petri dish.

Studio 6B at Rockefeller Center has become a laboratory for the 21st century talk show, and for a Facebooking generation, where Fallon will experiment, fail and succeed as host -- perhaps all three on the same night.

When we first spoke with Fallon in November, he said his show would stick to the talk show format perfected by Johnny Carson four decades ago: monologue, desk comedy bit, two guests and a band.

But beyond that, what can we expect? For one, an Internet presence like few talk shows before. Even before a single episode had aired, Fallon had already taken advantage of the Webocracy.

Through polling on the show's website, the Web audience selected the new Late Night logo. Fallon has solicited his Twitter followers for jokes (his handle is jimmyfallon), and viewers will be able to talk to him through Skype -- the Internet phone and video service -- during tapings. The show's website is staffed by three full-time bloggers, who compile viral videos, post photos and the sort.

"I think a lot of shows don't use the Internet as well as they could," said Fallon by phone earlier this month before a test show taping. "We want to make it so you could enjoy Late Night With Jimmy Fallon in as many ways as possible."

The 34-year-old Fallon has also become a prolific Twitterer (yes, it is him sending Tweets from his iPhone). It was through micro-blogging that Fallon announced his first guests: Robert De Niro, Justin Timberlake and Van Morrison performing from Astral Weeks.

"It's almost like therapy, Twitter," Fallon said. "You can't go past a certain amount of characters, so no one really gets boring. No one can get on a soapbox and go off."

Then there's the matter of his comedy. If talk show history is an indicator, we know this: Whereas The Tonight Show, dating back to its Steve Allen days, has maintained its buttoned-up tradition of topical comedy, Late Night has always ditched the tie and loosened its collar (or replaced it altogether, as David Letterman famously did, with an Alka-Seltzer suit).

We know Leno is the comic, Letterman the dry-witted curmudgeon, O'Brien a cartoon character, Kimmel the frat guy and Ferguson the stream-of-conscience monologuist.

Fallon? From his six seasons on Saturday Night Live, we've come to know him as the baby-face comic with the elastic voice and manic stage presence and aloof, boyish charm. He does impressions. He's known to giggle in scenes and break character. He comes from a sketch comedy background but has performed stand-up in recent months.

Marquee guests and curiosity would likely boost Fallon's ratings for a while, but long-term success will come in setting himself apart from a crowded late-night field. When O'Brien took over Late Night 16 years ago, it was him, Jay and Dave. Now there's the Jon Stewart/Stephen Colbert tandem, Kimmel, Leno's moving to prime time in September and Fox is entering the week-night game with former-Seinfeld writer Spike Feresten.

Of immediate concern: Fallon will have to fend off the encroaching ratings of CBS rival Craig Ferguson, who overtook Conan O'Brien in viewership for the first time last April.

"I'm not thinking about Craig Ferguson, I'm not thinking about Jimmy Kimmel," Fallon said. "My biggest competition is sleep."

So when Fallon says, "I'll do anything to get a laugh," it sounds like as much of a warning as a promise -- which for the generation of 140-character attention-spans tuning in, might not be such a bad thing.