Brent over at KC Dog Blog has an excellent piece discussing the results of a recent study on dog aggression based on breed. Of particular interest is Pit Bulls. Turns out they rank as one of the most people friendly dogs around. However, Pit Bulls don't do so well with other dogs, about the same as Chihuahuas and Jack Russel Terriers.
What's even more significant, though, is that there is a wider variance within any particular breed than there is between different breeds. In other words, whatever the breed reputation, there is a good chance the dog won't fit the stereotype. Which just goes back to what most sane people have been saying all along: each dog deserves to be judged on its own merit.