Here is my 2 cents worth: I've tried at least 6 or 7 "registry cleaners"
and have deleted quite a lot of uneeded or redundant keys.

Fortunately I've done no harm to my system. However, I have not found that
I've experienced any performance enhancement.

I think the idea of an automated cleaner sounds great ... if it is safe and
effective. But for me, the risk benefit ratio cannot justify using any of
the registry cleaners that I've encountered so far.