I updated to RC3 3170 briefly (Mac Pro, 3GB) and it caused serious problems immediately. Even after installing the new version of Parallels tools and rebooting both Parallels and OSX perfromance takes a serious hit. Many operations, especially closing windows on the screen or shutting down Windows XP, cause OSX to hang for a while with the spinning beach ball. I downgraded to 3150 and the problems went away. Looks like 3170 isn't really ready yet... 3150 has been completely stable so far. 