I wasn't going to fix my Pitbull (gone since summer of 2011), because the only behavior being intact caused was his habit of humping his bed. Apart from that, he was about as good a dog as anyone could hope for.
The vet talked me into it eventually by telling me that it would make fixed male dogs less likely to attack him, which was a problem I was having. As I said earlier, that actually didn't work. They still attacked him.
I think he was attacked so often because of how he held himself rather than because he smelled of testosterone. When a dominant male would come by, he'd usually expect other male dogs to expose their bellies and wag their tails, and that would prevent being attacked. My dog held his head high, and ignored dominant dogs that came over to him, which seemed to enrage them into attacking him. So there was no reason at all to have had him fixed. Wasted pain and money.
