FYI, pit pull's are usually very PEOPLE friendly. And they are generally fine with other dogs as well. You see pit bull's in flyball quit a bit as they are short and fairly quick - first dog in this video is a pit bull and is part of a household of probably 8+ other dogs:
Lots of other dogs around during tournament - no more problems than any other breeds.
They are also usually very family friendly dogs - quite docile/lazy and very *protective* with kids. However, that trait makes them extremely aggressive with other dogs that they perceive as threats to "their" humans.
Note: yes these are generalizations. Pit bull's trained to fight are an entirely different beast (as is any animal cruel people have had a hand in raising...).
In short: while some pit bulls may be aggressive for whatever reason, don't paint the whole bread with the same brush.