Ah, there's probably considerably less than you'd imagine. LAst year (2006) there were only three that I knew of. I had seen one, I was one, and I had heard of one more.
Vincent, while being an awesome character and an amazing costume, is not really that frequently cosplayed (not around here anyway), as his attire has so many complicated parts to it. I had a blast with it though, and may return to it this year, but I'm also doing another one.