I've just had my two bucks neutered... I was advised to take them for a check up before they were due to go in for their operation to see if they're healthy enough for it, and to see if the testicles had dropped. They were then booked in under the advice that they had to eat and drink up until the operation (rabbits can't vomit). The procedure involves removing their testicles, and all that will be aparant afterwards is a small scar from the stitch, and swollen testicles (which, I am told, will go down within a week or so).
When they came home, as they're house rabbits at the moment, we had them resting only on a blanket, in their litter trays we've used paper instead of the litter we usually use (megazorb) and you've to watch that they eat, drink and poop... which they may not for a few hours after the op, but it's important to try and temp them. They will be sleepy, but many rabbits would refuse some nice greens.
I'd much rather go through a neuter than a spay anyday.