http://www.pctools.com/registry-mechanic/insight/view/fix-registry/  Why registry cleaning and repair is important.

http://www.delete-computer-history.com/fix-pc-registry-problems.html  General information about fixing registry problems.

http://www.pcfixreview.com/  Review of PC registry problems and repair

http://en.wikipedia.org/wiki/Registry_cleaner  Registry cleaner concise description and information

http://askbobrankin.com/do_i_need_a_registry_cleaner.html  Registry questions, facts, links, and blog posts.