I have (in the past) come across some registry cleaners that were more dangerous than anything, which is why I always make a backup BEFORE doing anything with the registry. Now as much as I hate Symantec, their registry cleaner (2005) works pretty good. But you really need more than one registry cleaner. Like anti-virus software, one may not catch something another will.
I also use Eusing Free Registry Cleaner, and I've been very impressed with it so far. It picks up a lot of stuff that Symantec's don't, plus it backs up/restores the registry.
I've never had either one of these cleaners ask to remove a registry entry that was vital to the system. I've had them show some things that would affect preferences/history of a few programs, but Eusing also gives you the option to add them to the ignore list and never list them again in the scan.
I'm very careful, even though I trust both these programs, I still check all the entries to make sure nothing important is listed. I've also heard good things about JV16. They have a nice suite, but I like to pick and choose apps, don't care for suites too much.
I filed a complaint with the FTC on Max Alert, the a__wipes....
I do a registry cleaning/system backup every Friday. Something I learned years ago, the 3 golden rules for computers, they are 1. Backup. 2. Backup. 3. Backup.
It has saved my buns many times.....
I do know for a fact that a cluttered up registry will bog a computer down to a standstill, just like a fragmented hard drive will do. I keep my puter running in top condition at all times, and it is faster than greased owl crap.
The last reg cleaner reviews I read (independent) put Registry Medic below a couple of others. But that's subject to change every other month as new releases come out. I never, ever read reviews from the company's web site until I've read independent reviews. Some of these companies will have their own reviews plastered on a bunch of other web pages that was just an oversized ad, so you have to be careful about that too. It pays to research, at least most of the time. Max Alert pulled one over on me for the first and last time....
Another program I use is called RegCompact.net. It removes all the unused spaces out of the registry, makes it much smaller and faster. Good program, I use it every Friday like clockwork.
I'll bet Mouser could hack out a registry cleaner that would blow them all away...
Hmmm, perhaps some of this should go in the reviews/suggestions section.