Saw Bill Gates at AAAI-2001 in Seattle. Well, closest was about 100 feet away though
I saw Diana Krall at a concert (New Orleans Jazz Festival) and got her autograph on my Love Scene CDs (yes I'm a show-off
Also met in person Jacqui Naylor at a recital of hers in New Orleans.
In New Orleans at a Mardi Gras I saw Stevie Wonder on one of the main floats.
Saw Sharon Stone getting into Pat'O Brien's in New Orleans on 1996. I even talked to her and asked her if she was Sharon Stone (duh, how original), no surprise she said no and run away quickly without turning
Not sure if concerts/events count that much: Sting, Metallica, Godsmack, Perfect Circle, Dr. John, David Copperfield, and several other musicians/performers in Pensacola and/or New Orleans that I can't remember right now.
At the Miami Airport I saw a girl that I'm pretty sure was Franka Potente (from Lola Run and Bourne Identity)