I've never had a problem with CCleaner, but I follow one rule. CCleaner's makers seem to have done a pretty good job of putting anything that one shouldn't mess with (unless they REALLY know what they are doing) under "Advanced". So, I simply never delete anything in that category. As long as it's not in the "Advanced" category, I believe that the worst you can do is lose some history, logs, or cookies that save log on information for you on something that you may have wished that you kept.
Please note that I am only referring to the "Cleaner" category; not the "Issues" category. Good luck!
Edited by rlprlp, 09 July 2007 - 09:09 PM.