Please go read this PRO pitbull site.
www.pitbullpress
This is a site that LOVES the pit bull terrier. Please read the article on the dog park. It isn't a myth that they are not good with other dogs. And they do explain it very well in that article.
I am not picking on the breed itself, I still stand by what I said about not letting mine play with any big dog I didnt know. But the original question was about a pit bull.
After reading some of the responses I get the idea that most people are not aware that these dogs can go from being dog frendly to dog aggressive for no particular reason.It is in their GENES, you cannot change that with loving them.