I met Russel Howard a little while back while I was shopping at tesco.Didn't say much though was a little bit star struck.
As for other major celebs not really. Youtubers I've spoke to though are;
Tom Ska form asdf, All of the red vs blue voice actors, A little less known one but i spoke to MasakoX, who is the voice actor for goku in DBZ abridged
Oh almost forgot but I did have a nice chat with the actor who plays Sid in skins series 1