While in 2007 they feted their 21st birthdays at an intimate dinner at the Chateau Marmont, this year Mary-Kate and Ashley Olsen opted for a far more public celebration — the duo partied with more than 100,000 people at the Bonnaroo Music Festival in Tennessee over the weekend. The twins, who turned 22 on Friday, reportedly arrived in Manchester on Thursday, and were subsequently spotted downing diet Red Bull and Patron at a local bar. They spent Friday evening playing dinner host to 11 friends (and one surprise guest, Josh Groban) at the Hermitage Hotel, before heading out to the My Morning Jacket show at midnight. Their rock'n'roll weekend continued on Saturday, when Mary-Kate and Ashley rubbed elbows with Bonnaroo revelers at the Jack Johnson and Pearl Jam shows. By Sunday morning, the duo was ready to head home — but not before making a quick Starbucks stop on their way out, of course.