Jake T
Running With The Pack
Yes I would never advise using one of those programs, they are rubbish. I used one years ago on my ancient win 98 machine and it was never the same afterwards. You are far better off just doing a clean reinstall of your OS if you think it's slowing down noticeably.
If you do use a registry cleaner, make sure you back up the registry first. Or better yet, image your machine first.