I've been to one anime convention in my life: Anime Expo 2006
Saw CLAMP
Watched Patlabor 2 just a few feet away from head mech designer Yutaka Izubuchi
Met Noboru Ishiguro, director of LoGH and Macross:DYRL
Still, my favorite moment of all was pulling up to the video room and watching Slayers Great with a bunch of people who really enjoyed like I did.
I've never gone back because I can't top that. Such a good feeling.