One of the many oddities about attending even a first-rate film festival like AFI Fest in a company town like Hollywood is the disparity between the offbeat indie fare on offer and the enveloping mainstream smog that hazes over everything in this town. An example: Driving into downtown Hollywood to get to the AFI Fest's home at the ArcLight Cinema, you have to pass what feels like about a million skyscraper-sized advertisements for Fred Claus ("Oh great!" the mind screams. "Just four years and we've already got a remake of Elf'!”).

There's Vince Vaughn on a Big Wheel tricycle cackling like a fourth grader. Here's Vince Vaughn looking nonplused while green-wardrobed pixies use his head as the base for a human pyramid. You park the car, rush into the theatre, and the lights go down. Visions of Vince Vaughn-shaped sugarplums dance in your head while you're trying to read subtitles. It's an odd feeling.

And then there are the celebrity sightings—a constant in L.A. but far more plentiful at a film festival than under normal circumstances. These generally fall into two categories. Type A are the famous people just looking for something to do. Because actually being famous doesn't necessarily have to occupy a lot of your time—for a lot of stars it's more of a condition, like acne. And then there's Type B: the famous people who are hyping indie product.

Indie product is often used by mainstream artists as a kind of integrity shower: They wipe away the philistine grime of being in movies like Fred Claus by accepting scale for roles where they cry a lot or do something unlikable or get addicted to hard drugs. Even if the art movie tanks, the artist has, as they say, "made a departure" and "shown range" and can therefore breathe a sigh of relief and rest assured they're not getting pigeonholed as they sign that deal to do Fred Claus 2.

And so it was that as I left the journalist's lounge a Type A celebrity sighting occurred—one of the first rank. I bumped into Paris Hilton on a staircase. She wore no makeup and was completely unaccompanied except for the cell phone she carried in one hand and the small lapdog she cradled in the other. I'd like to say I was impressed or even struck dumb by my encounter with greatness, but the person I was with had to point out to me what a major celebrity moment I had just had—Paris was dressing down and looked so unlike herself I barely noticed her, even though we basically came face to face. For the record, and contrary to the infamous South Park episode, Paris' dog did not seem in the least suicidal.

Further down this same enchanted staircase, Jack Black was walking along with a small entourage—a perfect example of celebrity attendee Type B as he prepared to appear at an AFI Fest screening of Noah Baumbach's new picture Margot at the Wedding, which he stars in. Black is actually terrific in this film—something he has not been onscreen since School of Rock by my count.

As a nebbishy failed musician in the throes of a premature midlife crisis, Black pulls off two out of three in the indie trifecta: He cries a lot and does something unlikable, but he does not become addicted to hard drugs. More importantly, he has successfully "made a departure" and "shows range," outperforming such heavyweight emotionalists as Nicole Kidman and Jennifer Jason Leigh to do so.

In our magical staircase encounter, Jack's hair was dyed the yellow of cheddar cheese popcorn, and he appears to be carrying around another 30 or so pounds, giving him the appearance of a latter-day John Candy. Hopefully it's for a role. As Perez Hilton.

My favorite celebrity encounter of the AFI Fest so far came in the context of last night's world premiere of the hip-hop documentary Public Enemy: Welcome to the Terrordome. Flavor Flav revealed his presence in the audience by yelling back at the screen when the otherwise worshipful interviewee Henry Rollins suggested that the VH-1 series Flavor of Love was, er, perhaps not the way he'd like to remember such a pivotal member of the band. Flav was in full rebop mode at the Q&A afterward, mixing stream-of-consciousness monologues with clever non-sequiters to the packed theatre's delight.

But it was Public Enemy’s uncontested leader Chuck D. who (characteristically) punched through the general complacency and hero-worship of the whole celebrity trip by launching into a well-reasoned diatribe against the film American Gangster on the grounds that it celebrates a crappy and villainous black "role model" and pointed to Tyler Perry's Why Did I Get Married? as the kind of movie about the black experience white Americans ought to flock to see. In the content-free zone of celebrity sightings, it was a rare moment of depth and heft, and a reminder of the kind of challenge to received wisdom festivals like AFI were made to celebrate.