I work at a number of Anime conventions, and I used to cover horror movie conventions as a journalist, and my experiences with both in terms of the guests have always been pretty positive.
I'm not much of an autograph hound. I've been lucky enough to do things like drink with Lance Henriksen and have dinner with Rudy Ray Moore, and that, to me, is a lot more appealing a thing to have, if only in my memories, than an autograph.