GURPS works great for conventions, if planned well.
The best written description of planning for running GURPS at a convention that I know of comes from our own Mook, who has written quite a bit on it (and done quite a bit of it):
http://www.themook.net/gamegeekery/c...y/conventions/
I highly recommend reading his "Beware the Boogeyman" posts, which detail his most recent efforts toward creating and running a GURPS convention game. It starts here:
http://www.themook.net/gamegeekery/c...-boogeyman-01/
For those in a hurry, he has some Quick-Play Aventures available:
http://www.themook.net/gamegeekery/s...ay-adventures/
He also has some help with creating Quick-Start Characters:
http://www.themook.net/gamegeekery/m...rt-characters/