In reply to GridNorth: Until I became a Windows App developer, I was very much with you. But now I understand a bit more about the registry, I don't really understand what the fuss about it is. It serves a very useful purpose for apps and even when very large is very quick. In itself, it is not the cause of your PC slowing down.
The genuine speed gains you can make on your PC are by only running programs and services you need. We get really fed up when Registry cleaners decide that all the registry entries our program legitimately creates and uses get "cleaned" in the name of efficiency. And then we get the blame. Same goes for antivirus software. If you don't click on pictures of fat women, you don't need them.