Registry Repair:

You can either use regedit to fix a problem yourself or use one of the utilities to repair it. Although, using regedit can be dangerous, if you find a simple solution like removing a specific registry key, it may be safer than running one of the programs below which may change other things not related to your problem.

Recommended registry repair software:
CCleaner, Advanced System Care (ASC) both free.
Uniblue RegistryBooster - Can reindex which will do some speedup for free.
$40 to clean-up. People I talked to said this isn't worth it.

Comments on cnet forum Dec. 2009:
R. Proffitt says: "Those 600 problems reported by Registry Booster are likely little things and NOTHING that matters. For now, the consensus is that none of the registry fixers are any good."

msgale says: "About every six months this issue gets resustated. The same answers are given, nothing changes. Some say they are the best thing since bread, others say they are junk and don't work, some say they cause problems.
There is no answer."

rbsjrx says: "The simple truth is that there's no technical reason why someone who understands the workings and limitations of Windows registry system can't write a perfectly safe and useful registry cleaner utility - and some do.

msgale says: "Dr. Mark Russinovich is a Technical Fellow at Microsoft, who has written extensively about Microsoft Operating System internals and has access to Microsoft source code, does not believe it is possible to write a viable registry cleaner."

Other comments:
Every time you install a new program and then remove it, you're going to be leaving loose ends all over your registry...the best way to clean your registry and feel good about it is to totally re-install, and just put back the programs that you're using now. Most programs do not do a full job of cleaning up everything that they do the registry, and also leave stuff all over your system.
  The best way to avoid registry problems is to keep the registry clean and Revo Uninstaller. In it's extended removal mode, it gets rid of every trace of the removed program.

It has been noted that reg. cleaners in general should be used seldom and not during any noted system problems. If you have NO problem now, then use a cleaner. However, I strongly recommend CCleaner.

Most will give a technical description of specific problems, which requires some experience to determine whether or not you want to fix them.

I have found only one that I will use, PC Tools Registry Mechanic, but even the best can make a mess of your PC if you don't know what the function of the entry does.

rbsjrx commented: "Registry cleaners are over-hyped and a poorly designed or written one can cause much more harm thn good. IF (and that's a big "if") you need to use one, stick with IOBit Advanced System Care (ASC), CCleaner, or Uniblue's Registry Booster.
  Of course (I just have to say this), the very best defense is to not run Windows at all. Neither Linux or Mac OS are subject to the problems of Windows. They're more secure (and therefore less of a target for malware writers), don't need defragging, and have NO registry!

A PC consultant friend said: "I have not found any truly serious problems resolved by any registry cleaner. I haven't found any reg cleaner to make a marked improvement in performance either." Art