Fascinating post. I've known about the Bonobos for a while now. Was not familiar with the other examples.
I think the more fascinating thing here, in some respects, is not so much the homosexual behavior but the fact that other animals are having sex for pleasure at all. Though I guess it really shouldn't be too surprising to anyone who's had a dog hump his leg...
Yeah, it's a pretty fun peek into our evolutionary history when we realise the social/bonding function sex serves in other species. Even weirder, the Macaques have been found interacting sexually with deer recently...