I have fitted an FG rear shock to my 99 R1. It has improved it out of site. The shock is 23mm longer than standard so it makes the bike turn in much better and it holds a tight line now where it used to push the front end and run wide. It is set with a heaver spring but less preload so it is more complient over the bumps but is not prone to squat under power. The damping is much better as well.
The other benifit i have noticed is it shakes its head less now than before (i dont run a steering damper). Mostly it only shakes now as the front wheel comes back to earth while still leaned over on the exit of long sweepers. Yahoo.
If you are looking for a good shock i recomend you consider one of these. I will try to post a pic later of it but it looks like a WP with a blue body and spring.