The smorgasbord of Bonnaroo began in earnest Friday with a packed slate highlighted by the rarest of double bills: Chris Rock followed by Metallica.

It was to be the first appearance for both at the Bonnaroo Music & Arts Festival, held annually south of Nashville on a 700-acre countryside site. Neither is exactly standard fare for the festival, which began in 2002 as primarily a jam band event. But in recent years, Bonnaroo has broadened and drawn a crowd more diverse than just hippies.

Still, how Metallica (a big draw this year) and its black-clad fans would mesh with the festival's laid-back vibe was a big question Friday. Also much-discussed was whether M.I.A., the British electronic dance-hall rapper, would show. She recently canceled her upcoming European tour because of exhaustion from touring, but was still expected to perform her Friday evening set.

The notorious Tennessee heat that has in the past made Bonnaroo a chore was thus far bearable. Thundershowers were expected Friday night and Saturday.

Usually sold-out with an attendance of 80,000, this year's Bonnaroo hadn't yet reached capacity, but was overrun with tens of thousands of fans who came from far and wide to camp through the weekend.

"So is everyone having a nice communal experience?" Vampire Weekend lead singer Ezra Koenig asked the crowd. He later added, with perhaps some sarcasm: "You guys, I'm sure, have a full weekend in store of discovering yourselves and others."

The New York-based indie band Vampire Weekend was part of the relatively thin Thursday night slate that also included several comedians, a tradition of Bonnaroo. Janeane Garofalo and Zach Galifianakis were among those performing in the circus-style comedy tent.

"They asked me if I wanted to perform at Bonnaroo and I said, `Will there be a circus tent?'" joked Galifianakis. His comedy often intersects with music; he plays piano during much of his act and he's starred in music videos for Fiona Apple and Kanye West, who's performing late Saturday night at Bonnaroo.

Garofalo said the challenges for a comedian in such an environment can be many.

"Nothing is better for comedy than doing it during the day, having this kind of noise behind you and doing it in a circus tent," she joked.

Also to play Friday were the Raconteurs, Willie Nelson, My Morning Jacket and the Swell Season and the duo of Irish singer-songwriter Glen Hansard and Czech pianist Marketa Irglova _ the stars of the film "Once."

Hansard said he's still adjusting to being the co-winner _ along with Irglova _ of the Academy Award for best original song ("Falling Slowly" from "Once").

"It's a new personality to try on or a new set of clothes to try on," said Hansard, who was less famous as the lead singer of the Frames. "Everything you've been is basically over. ... Sometimes it feels more comfortable having potential rather than having accreditation."

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