Summer of '02 I worked at a summer camp and DM'ed for some of the kids there. At the end of the summer, they got the camp director to call me up to his office on some pretext, then they decorated the computer room where I worked, yelled Surprise! when I came back, and had this huge chocolate cake that said World's Best Dungeon Master on it. That was very cool.
When I was in high school, we would have marathon D&D sessions on the weekends, but we always had to break for dinner at individual houses, this being the family-values midwest and all. Anyway, one of my best friends, he would always go home for dinner and be back in less than ten minutes, ringing the doorbell and wanting to restart the game already.
And then there's my current group... who just say, "That was fun," or, "You're a good DM," things like that. It means a lot!