I purchased Parallels 4.0, but decided to stick with 3.0 after reading the horror stories switching to 4.0. I did allow 3.0 to do it's update to build 5636 yesterday. I wish I hadn't though; it didn't fix any of the problems I was having, but did pop up an advertisement for 4.0 on me today. This ad crashed my Windows session, and left it eternally spinning the Mac beachball. Had to reboot. Lost work. Unless 5636 fixes some problem for you, I'd say avoid it.
