I am in the same camp as most regulars here who wouldn't advise someone to use a registry cleaner in order to boost a PC's overall performance/speed. No one has ever been able to provide solid evidence to back up such a claim. That being said, whenever I caution people not to use these programs, I normally add that sometimes these cleaners have been known to cause a situation where the PC becomes unbootable. I seem to remember reading a number of posts in these XP newsgroups from people who have reported this behavior. But now I wonder. (Memories often are not reliable!) I do value evidence. But I Googled for instances where this sort of behavior happens and I couldn't find anything convincing! The closest I could find was this post: http://forums.comodo.com/comodo-sys...stem-being-unable-to-boot-t38353.0.html;wap2= And newsgroup archives? Just a few hits, _total_: http://groups.google.com/groups/sea...ner"&btnG=Search&sitesearch=groups.google.com (arguably I could have opened up the search, but 5 results?!) Then again, Google is nowhere near as good as it once was when it comes to searching archived Usenet posts. But was I imagining posts mentioning these occurences? I still won't be recommending these programs since, again, there is no evidence they are beneficial. I would imagine if someone is overzealous, real damage could occur (just like with regedit). But if someone could point me to some posts where someone actually did have the behavior described (i.e., not able to boot after running a registry "cleaner" or "optimizer"), I would appreciate it. Otherwise, I will have to stop making that claim. (However, until someone provides *real* evidence that these cleaners boost performance, I will continue to make the claim that the evidence for *that* does not exist.) Evidence is evidence, and I feel that my advice is more valuable if it is not tainted by unfounded opinion.