My mother was in Tivoli Gardens in Denmark and ran into Morgan Freeman.
A teaching assistant for one of my classes in middle school was dating Josh Hartnet, and he came into the classroom once.
I saw Michael Moore walking down the street by my dad's house without any kind of entourage.
My friend's dad was Phil Hartman, and since that whole incident with his mom killing his dad and then shooting herself, he got a lot of sympathies from Matt Groening who picked him up from school a couple of times.
My mom's friend is Ralph Nader's cousin, we met him personally after one of his rallies in Minneapolis.
It doesn't so much count as celebrities in the traditional sense, but when I went to the Heathen Crusade II in January, I was taking the shuttle from the hotel to the venue, and everybody on the shuttle were in the bands Rudra, Skyforger, Obtest, and Manegarm! We talked for a while.