There is some debate over whether or not CCleaner or any other program increases the speed of your computer by messing with the registry. There is however plenty of evidence that it/they have done harm. Use them for temporary files and cookies if you want rather than the built in tools of the operating system but do not use them to mess about with the registry. Microsoft themselves do not supply a registry cleaner for their own registry. In fact there is no such thing as "cleaning " a registry. You would likely get better results cleaning the vents with an air duster.