Aside from actually just seeing people on the street, I have very few famous people interactions and most aren't tabloid worthy.
I did meet (briefly) Hamish Linklater through my sister who knows him through acting. He's the brother on the New Adventures of Old Christine.
I also played spin the bottle with the lead singer of the Decemberists once - actually we grew-up together (same elementary, middle, high school), so we hung out in theater class, plays, and a few parties in high school and college. They aren't that popular outside Seattle area, though, so I doubt anyone really knows who he is.
I thought I met someone else, but can't remember now...