updated 07/18/2005 AT 01:00 AM EDT
•originally published 07/18/2005 AT 01:00 AM EDT
Sir Paul McCartney, who opened the London show with U2, stayed in the wings to watch Snoop Dogg and the Brit band Keane. Marvels Keane singer Tom Chaplin: "We found out he'd been singing the entire way through all of our songs!"
American Idol judge Randy Jackson, who played bass for Mariah Carey, enjoyed the celeb overload: "I am standing there talking to Brandon Rowers, the singer from the Killers, and I get this hug from Joss Stone, then I feel somebody tickling me and it's Brittany Murphy. Everywhere you look you run into Brad Pitt. It was like being in the warmest environment of great talent ever on the planet." (He also got some love from McCartney during rehearsals: "Paul McCartney was checking me out, dude, and he liked it! I was judged by Paul, dude!")
Brad Pitt bonded with McCartney, Snoop Dogg and soccer superstar David Beckham and also bumped into former fiancée Gwyneth Paitrow and her 14-month-old daughter Apple, whose face was covered with ice cream. "He ruffled Apple's hair, and he was stroking her cheek. They were both laughing about what a mess she was," says a witness. Meanwhile Paltrow's husband, Coldplay frontman Chris Martin, stood nearby chatting with UN Secretary-General Kofi Annan.
New couple Scarlett Johansson and Josh Hartnett were also in London, although if s unclear whether or not they actually saw any of the acts. "They were on their own, very lossy," says a backstage source. "She was on his lap and kept burying her head in his shoulder. They were clearly very loved up."
For Madonna the concert turned into a great networking opportunity. Upon spotting actor Ricky Gervais, the boss-from-hell on the BBC series The Office, the singer hit him up for a part.
Meanwhile, in Philadelphia, actor Chris Tucker—who brought his son Destin, 6, and flew into town with a copy of the Declaration of Independence—made the rounds with Will Smith, Russell Simmons and Rev. Al Sharpton.
Philly also provided the venue for a meeting of the hair bands Def Leppard and Bon Jovi, who autographed a car for charity and shared hugs, if not cans of hair spray.
At the end of the day, says Randy Jackson, though the mood was festive, the stars remained focused on the real reason they were all there: "It wasn't like some awards show or some promotional event. It was actually really to just give and help people that are struggling. It's the best thing I've ever been involved in."
Greg Adkins and Chris Strauss. Bryan Alexander, Courtney Rubin and Neil Michael in London and Sean Scully, Mary Green, Jennifer Odell and Tiffany McGee in Philadelphia