Well, I don't have an American Bulldog, but good friends of ours have two. A male and a female (not a breeding pair, they are bro and sis and are fixed). Anyway, these dogs are quite pleasant. Although, I wouldn't say that they are like boxers much in terms of looks or mannerisms. Firstly, they grow MUCH bigger than boxers. Secondly, they do not have the stamina boxers have. My Emma tires out her buddies rather easily (in fact, the few altercations between them have occurred after Emma had worn them out). I guess that the females might resemble boxers slightly, especially if they're not standing right next to one another. The males are just so big that I can't see a resemblance.
I think ABs are prone to many of the same problems as other large breeds: arthritis, hip dysplasia etc. Also, they are headstrong and physically strong so would likely need a decent amount of obedience training. That said, I think they can be great pets. We love our friends' ABs...check out my gallery. You can see pics of them, at Emma's b-day party. At that time, they were only 8 1/2 months old.
Amanda