I've been doing conventions for the past 12 years... so the short answer is yes, and quite a lot of people. Outside of conventions, I've met a couple of people at a play (Alyson Hannigan who was doing the play, and Jason Priestley who was just in the audience - probably because Luke Perry was also starring in it, but I didn't meet Luke in person), a couple outside their hotel when they were in town.
For the full list of people (right now I'm at 185), I'll just
link my website... and for photos, I'll also
link my website because there just are way too many of them.
I've mainly had some really pleasant encounters with them, some longer than others, some shorter than others. Some of the really nice ones include Clare Kramer, Felicia Day, Nathan Fillion, Eliza Dushku, Sean Gunn, Anthony Head, Catherine Tate, Arthur Darvill, David Bradley, Richard Dean Anderson, Amanda Tapping, James Marsters, Juliet Landau, Amy Acker, Andy Hallet, Jewel Staite, Morena Baccarin, Summer Glau, Neil Roberts, Mark Sheppard, Dichen Lachman, Miracle Laurie, Holly Marie Combs, Brian Krause, Robert Englund, Aaron Douglas, Neve McIntosh, Catrin Stewart, Rose Leslie, Lea Thompson, Sherilyn Fenn, aaaaand the list is already growing way too long... Just know there are a lot of really nice and friendly celebs out there
The only encounter I would classify as "bad" was Michael Gambon (Dumbledore) who just mainly ignored the people coming to meet him.