I have heard that you should keep the registry clean on Windows. Is this actually important or is it just myth?
As I understand it, cleaning the registry is not going to really do much for your computer performance if anything. The registry contains thousands of keys and cleaning out a few dead ones won't really make much difference.
This forum post contains some sources that seem to confirm registry cleaning as a mythical performance enhancer.
It will have no effect on system speed. There is an excellent chance it will make your system less reliable.
The registry is a huge database optimized for speed. It doesn't matter if some game left its config options in there. Other programs aren't going to care and Windows can handle the memory usage just fine by paging (i.e. only loading what's needed) and other techniques.
The only time a registry cleaner could be useful is if a program was not uninstalled properly; in this case you might have some specific problem such as a broken file association. But if you are not seeing problems and are just looking for speed you are probably wasting your time. Not only that, but deleting stuff from the registry can break things in subtle or hard-to-fix ways. Hopefully a good registry cleaner backs up all its changes so that you can easily restore your old registry... assuming your computer boots properly after the cleaning.
If your windows system has lots of strange bugs that are due to registry problems you might be better served by re-installing. Before XP I used to re-install Windows every 6 months. Now I almost never have to do it. I would avoid registry cleaners.
I checked the Wikipedia page on registry cleaners.
Looking at Jeff's answer, maybe someone needs to update that with criticisms.
I have used CCleaner often, and in fact, also been suggested registry defragmentation tools.
Mark Russinovich, who I trust a lot with my Windows machines, also has a PageDefrag tool that works on registry hive defragmentation.
A reference to another tool by Mark called RegDelNull that helps to cleanup registry keys with embedded
I also often use RevoUninstaller to cleanup after some uninstalls.
The warning from Mark and others on the risk involved with cleanup should be and is taken seriously.
I've used PC HealthBoost with success on a few slow PCs. I chose it because it does work as advertised and is in good standing with Microsoft. Microsoft, itself, also used to make a registry cleaner called regclean.exe.
Basically, uninstallers sometimes are poorly written, and that sometimes creates errors in your operating system that show popup errors or blue screens. Also, have you ever right-clicked the desktop and found it takes a long time because the context menu has extra menu options from a product (like Norton Antivirus) and one of those menu items is still there but the product has since been uninstalled? That delay is aggravating, and contributes to the slowness of the PC. Also, when a PC boots, it is looking for file paths mapped to keys where those files were deleted by an uninstaller but not the key.
Some may say it's only a marginal slowness, but I've seen it be a significant factor with nothing more than 4 poorly written uninstallers, where some of these programs may have created dozens of registry keys.
A word of caution, however -- not all registry cleaners are alike. You want one that can backup your registry first before making changes, and one that doesn't delete legitimate keys. Some of these companies are cagey, but I've been very pleased with PC HealthBoost.
I'm probably not a typical user, but I've never done so and never seen a need to do so. However, I do know that pretty much every program you've ever installed leaves some kind of junk lying around in your registry and/or hard drive, so it's still possible that such utilities might have a purpose.
I agree, cleaning the registry risk vs reward is low, however tools to Registry defrag / compact the registry will increase performance. I use Registry Mechanic to just defrag and compact the Registry, not the registry cleaner options.
I believe it's better (effort and time wise) to just reinstall the whole system every 6 months or so, than spend every once in a while cleaning registry, "keeping the system clear" with anti virus, anti trojan, anti spyware, anti ... whatever you have left.
And the whole reinstall doesn't take more than 4-5 hours, including installing all software and customizing preferences in it.