I'd like to meet the head of the MC development team (is it still Notch?) and tell him how awesome the game is, but also suggest some improvements. I don't get much customer service by using the online support form or the bug tracker, or the official Twitter page, or the official Reddit page. Maybe talking to them in person will cause them to realize I'm not just some customer-ID number in a database, who bought their game, but rather a REAL PERSON.
Mojang developers occasionally go to other events, and you may be able to meet up with them at those events. For instance, Dinnerbone tweeted about attending MineVention back in April in Dublin, Ireland, and he and Jens also went to GDC in San Francisco back in March. If you are really intent on meeting them in person, you may just need to keep an eye on their Twitter feeds to see which events they will be attending, and determine how feasible it would be to go.