I *seen* dozens of celebrities at Southern California area shows going back to the late 70's but there's been only a handful notable for actually talking or interacting in some way. For U2, the winner has to be Woody Harrelson (who is apparently a huge U2 fan, having seen him in the pit at a couple Elevation and Vertigo tour shows as well). I've related this story on other U2 forums in the past so here it is again:
U2 - 1997 LA Coliseum Popmart tour. Since the ZooTV tour, I had been a member of U2's fanclub and got great tickets for the earlier San Diego and this LA Coliseum show. We had 4 seats in the 9th row right next to the walkway going to the B Stage this show. My wife, my brother and his friend went with me.
After opening band Rage Against The Machine's set, this couple and their little 6 or 7 year old girl take their seats behind us. When U2's set starts, my brother and his buddy leave to sneak all the way up to the front while everyone else is standing on top of their rickety folding metal seats to see the stage. The guy behind us climbs over his chair and takes my brother's seat standing next to me. Over the very loud sound, he asks me if it's alright to stand on my brother's empty seat and I tell him no problem unless he comes back. I'm really focused on the show so I don't even note who this guy is next to me.
Meanwhile, my wife is going nuts trying to talk in my ear over the band until I finally hear her say "that's Woody Harrelson." He was pretty cool and definitely into the show but things took a bad turn when he starts getting high while his Asian girlfriend or wife and their young pre-teen daughter look uncomfortable as hell left in their seats in the row behind us. My wife starts going ballistic about Woody getting fucked up while the kid is actually trying to uncomfortably go to sleep across a pair of chairs. At some point, some other people around us finally clue in to who he was and are staring at him instead of watching the show which clearly made him uncomfortable and they left just before the encores.
Non-U2 shows where I've *met* celebrities include:
Van Halen 1980 LA Sports Arena during the Women And Children First tour. I had tickets about 21st row floor. We were sitting right behind McKenzie Phillips and her date or boyfriend who looked like a sleezy drug dealer (which he probably was). I'd guess at the time co-star Valery Bertinelli was already dating Eddie. They kept doing lines of coke off her compact mirror outta her purse before the show started and my buddy was giving them shit about not sharing and ragging on the guy about coke fucking up people's faces (both had real bad acne). They wound up leaving before Van Halen even came on.
Van Halen - 1998 Hard Rock, Las Vegas. I didn't really think much of the July 4th Devore, CA show they played with new, 3rd singer Gary Cherone but on a spur of the moment ticket purchase a day before the show, a nabbed a 7th row seat to the 2nd show of a 2 night stand in the relatively small Hard Rock Theater.
So I do the drive to Vegas, wind up meeting a bunch of Van Halen fans from various on-line forums and that night, I have Valery Bertinelli, their son Wolfgang (who was about 7 or 8 at the time) and I guess his nanny sitting directly behind me. I had corresponded with Val a couple e-mails when she was on the Van Halen Mailing List and talked with her for a couple minutes before the show started. Very nice woman who remember congratulating me online about the birth of our son the year before. The show itself was great, far better than the Devore show and it was funny watching Wolfgang getting bored midway through the show and running around playing on the railing and running up and down the aisle with some kid buddy of his like they were in a empty movie theater.