I was a long time Pro V1x player and was always really happy with the ball. I did spend a large part of last year testing a number of different brands out there but ended up coming back to the ProV1 line. When the 2009 versions came out, I bought a box of ProV1x and was really happy. I read an article on how to find the best ball for your game and went out to the course to go through the "green to tee" fitting that Titleist recommends.
At the end of that session I ended up switching to the ProV1. I felt like I was getting better control around the greens, better feel on putts and a little bit of better performance from 100 yards and in. Also, I was only losing about 5 yards on my drives so it just made more sense to go with the ball that might help me with my scoring. At the end of the day, I really like both the ProV1 and ProV1x and won't be switching anytime soon.