Although I'm no longer vegetarian (my diet is still probably 75-80% vegetarian), this article about NFL tight-end Tony Gonzalez is a pretty good read for anyone that doubts being vegan (or for that matter vegetarian) is a hinderance to being athletic.
Who knows, maybe someday I'll go back to a vegetarian and maybe a vegan diet. But that's not until I've removed all the 'weird' meats off of my must try list.