ITreviewed posted a review on the Comodo Registry Cleaner

Comodo's Registry Cleaner is a really good program. It's fast, effective, and is a snap to use. And the fact that it's free means you've got absolutely nothing to loose. When we tested the software on our review machine it managed to improve its boot time by around 5 seconds. Total memory usage also dropped, which was also quite an improvement stemming from fixing 648 registry errors! It didn't harm our system in any way, either, which is the main thing. Another free registry cleaner worth testing is CCleaner, which also cleans traces of your online activities such as your Internet history. The only downside with CCleaner is that it's a 'mild' registry cleaner and does not go as deep as Comodo's Registry Cleaner. If you feel uncomfortable using free software for some reason, check out Uniblue's RegistryBooster 2009

Comodo Registry Cleaner Review