Agree with everybody here, but here is a suggestion: Don't use the registry cleaner that is bundled with it.
I realize that many people never had problems with ccleaner's registry cleaner, but my personal experience with the registry cleaner softwares have been horrible. The registry no longer makes your computer so slow as before. When windows NT was released, many of the problems with the old registry is no longer present. It is okay to have a spare key around here and there. What is not okay is to remove a registry key that actually does something. I speak from experience, in that many registry cleaners I have used, including ccleaner, has caused at least one problem. It stems from NTI backup not starting, disk cleanup destroying my user profile because there was a registry key keeping it from removing the system profile, game doesn't save settings, etc. They are really a headache, and I have experienced no performance improvement.
A majority of registry cleaners are scareware. I respect ccleaner for their product but my general tip is to examine what keys are being removed before you remove them. (note: that even in a custom install of windows 7, any registry cleaner will still pick up a few spare keys. It is absurd that perhaps, microsoft shipped the operating system with useless registry keys)