I have used TuneUp Utilities for couple years (now using 2012-version) and before that I used CCleaner... Never had an issue, but TuneUp has helped to get some corruptions removed from the registry (and it also does registry defrag, if that does any real difference...). Be aware however, that there are some "evil"-registry tweakers around... So, do some research before running any of these softwares! There is also some cheating softwares (even payload!) that first "broken" the registry and then "fix" it, so users are happy when they read how many thousand errors the software has corrected... Basically, if you are happy living whitout any registry cleaner/tweaker, do not try any... But if you are sure that you want to use them, do some research and do not believe anything on the software homepage...