I refer to Levar Burton because he is the reason I became aware of Twitter. About a year ago, a friend of mine called me from a bar to say - "Dude, I'm having lunch with Geordi Laforge.".
Turns out Burton was an early Twitter adopter, found himself in Toronto without plans and Tweeted that he needed a good lunch recommendation. From the responses, he picked a place downtown and invited his Toronto followers to meet him for a beer. The place was instantly packed with Star Trek geeks, my friend included.
Alas, the Twitter crowd is not so friendly and open anymore.