If you use Parallels 6 (for running Windows on a Mac) and update to Mac OSx 10.6.8 you may run into some problems. Here are a couple of links that may help you out.
Dock using 100% CPU after OS X 10.6.8 update for Parallels 6 users | MacFixIt – CNET Reviews
KB Parallels: Mac Dock consuming 100% of CPU core after upgrade to Mac OS X 10.6.8