Registry cleaners

Are registry cleaners worth using? Having installed and uninstalled many applications, games and demos etc I have noticed a definite slow down in my PC and I am wondering if a registry cleaner might be worth trying before I am forced to do a complete format and rebuild. Any particular programs that should be avoided or any very good ones to get?

Whilst we are on the subject I am about to step into the realms of overclocking, Zulu wants more power out of his PC but is not looking at upgrading for a few months yet so we are going to try some overclocking, he has a pentium4 3gig processor and 1gb of RAM do you think I will get much out of it?

I follow the tweak guides at this link:

There is probably more there than you need or want - including links to registry cleaners

I use this tool.

Thanks guys will give those a try

I use ccleaner (removed over a gig of crap the first time I used it) and Regcure as a secondry ‘fix’, work well for me.

I use them often (EasyCleaner and RegCure). That and checking the start-up programa really make a difference

I am using CCleaner, and I have the feeling it works really well, even better than EasyCleaner with WinXP