i have a girl who is desexed, she was really mean and bitey, then when her two tank mates at the vets were rehomed (no one wanted her she bit too much) we decided to put her in with two males after she'd recovered. well, noone wanted her still, so i took her home and shes now really docile, and gets along with all my other ratties.
im all for desexing myself, its a common practice here, especially for settling the rats down.
we do mouse desexing as well with good results. usually only male mice though. i dont have any desexed mice myself, but was thinking about it for later on when i stop breeding mice so my top boys can live with the girls in the 6 foot tank i have.