I am working on litter training myself. Black Jack is mostly litter trained, but as I have other rabbits around, he still leaves a few poops around. However, he stopped spraying almost the moment I had him neutered about a week and a half ago. What I did was found the corner of his cage he usually "goes" in and put his litter box there. I use the carefresh pet bedding as litter (and I sometimes use shredded paper, but they tend to eat that) I line his cage with fleece pet blankets and shake out any "bunny pellets" that miss the box at the end of the day. He never PEES outside his litter box anymore either.
During floor time, I have found that both the rabbits and guinea pigs like one particular corner of the living room, which is behind BJ's cage, to congragate and other wise use the "toilet." Knowing that it would be very difficult at best to stop it, I decided to go with it, and I put a towel down and another litter type box. They all use it, and tend to hang out near or in the litter box. The hay bin that is attached to BJ's cage is also the community hay box and will sit in the litter pan and eat hay at the same time. It has reduced the "clean up" quite considerably. That being said, I would also like them to be completely trained at some point.