One of the things I've always loved about book, movie, and comic book conventions is the things you can learn, the stuff you find (especially new talent you'd never heard of before), and the more unique and interesting fans. Just watching some of the people who come by is a social experiment in and of itself.
Take for example this guy who I ran into down at Kokomocon:
http://www.youtube.com/watch?v=ykb7U-PJMl0
He was quite the character and a lot of fun to talk to. Plus he did an awesome job staying in character the entire show. Then there was the different con goers who roamed the isles and were quite fun to talk to, get to know, discuss things with, etc. They're almost always a blast. I don't think I've ever really had a bad convention yet. Sure, sales might suck at a few, but overall you still come away with something good from each show.
Which then leads me to my next question. Which of you still goes to conventions, or at one time went to them, and what were some of the more memorable sights you saw there? IE, people, vendors, authors, artists, guests, famous people, cosplayers, etc.