My cat Louie is no longer intact. I'm hoping it won't change him too much. My other cat Silk is a lot more aloof now that it's been about a year since he was neutered, but it's hard to tell if it's because of the neutering or because the other cat harasses him if he comes too close to me.
Louie was at the vet's overnight and Silk was very clingy, so it's probably Louie who's the problem. We'll have to see how the 2 cats interact now that they're both neutered.