Below are some additional resources and information about
registry cleaners that you may find useful.
Windows
Registry From Wikipedia - a detailed and in depth technical
explanation of the windows registry and how it works.
Testing Registry Cleaners - A bit dated in the products
tested but still very good information about registry cleaners
in general from Information Week.
Why I Don't Use
Registry Cleaners - An interesting article about some
reasons people may not use registry cleaners at all with links
to additional sources of information.
Windows
Registry From Microsoft - This is Microsoft's description
(although pretty technical) about the Windows registry.
Registry Tutorial - A great overview of the Windows registry
form the computer experts at the Bleeping Computer forums.
Tweaking
The Registry - If you are feeling a little adventurous, here
are some tweaks you can make to your registry (for
technical experts only!)