I downloaded and installed v9 just tonight. I skimmed through the system booster > Optimize tool, and allowed it to run. One thing I didn't look into was the "cache" it was deleting from WoW itself. The program completely nuked my games config file as well as the lua files used by my add-ons that house all of the settings each of my characters, losing the entirety of my UI's customization. Do yourself a favor, un-check WoW from the cache cleanup to save yourself a huge potential headache.