I'm using Win XP Pro (up to date) and just updated CCleaner to v. 2.21.940 a few minutes ago. I admit that I made a mess a couple of days ago and had to restore my system; I've also managed to avoid learning anything about the Registry in all these years.
I've gone back to removing programs one at a time and running CCleaner. But yesterday and today, I can't seem to clean the Registry completely. I've been running the Registry cleaner all day today -- about 15 times, and re-booting about as often. CCleaner keeps coming up with one item at a time to clean. And they mostly seem trivial -