Update 2014: Microsoft has since finally posted their own take on the use of registry cleaners, and it’s quite clear:

Some products such as registry cleaning utilities suggest that the registry needs regular maintenance or cleaning.  However, serious issues can occur when you modify the registry incorrectly using these types of utilities. These issues might require users to reinstall the operating system due to instability. Microsoft cannot guarantee that these problems can be solved without a reinstallation of the Operating System as the extent of the changes made by registry cleaning utilities varies from application to application.

Bottom line: don’t use registry cleaners, and view any product or company which recommends that you do in a rightfully suspicious light.

(My original post follows):

If you’re used to my work, you know how strongly against the use of any registry cleaners I am.  It’s no secret that many experts, including Windows guru Mark Russinovich, warn of their dangers.  The fundamental reason behind this position is that no program can know with certainty what is and is not desired or necessary to be stored in the registry.  And plus, even if plenty of unnecessary stuff is contained therein, it’s not really beneficial to remove it.  The registry as a whole is relatively small anyway compared with the amount of RAM available on modern PCs, and removing even a few thousand straggling values or keys provides very little, if any, performance improvement.

So in light of this, today I’m here with an update regarding one of the most popular posts I’ve had on this blog to date, and I felt like it deserved its own post thanks to the magnitude of the example.  In my Click2Run Configuration Failure Office 2010 post, I offer a solution to a fairly widespread and rather maddening issue with Office 2010 Click2Run installations suddenly failing.  Not even Microsoft has addressed the problem with an official solution to date, so this blog post has gotten plenty of traffic.

One thing my post didn’t include, however, was a known cause for the problem.  Well, as with most computer problems, this error doesn’t just spontaneously appear.  It’s now become apparent to me that the culprit behind this problem is actually registry cleaning applications.  The most commonly seen program responsible for this problem appears to be iolo’s System Mechanic, but it’s safe to assume that any registry cleaner could lead to the same results.  For a long time now, I have been recommending against the use of this program and have removed it from many of my clients’ PCs following consultation with them regarding its use.  If you have System Mechanic installed and have been using it, you can expect that you might run into the same problem in the future.

This is just an example, of course.  Although it’s now mostly certain that this is the predominant cause of this irritating Office 2010 problem, registry cleaners can just as easily lead to any number of other issues that are hard to diagnose and potentially impossible to troubleshoot.  Save yourself the headache and remove any registry cleaning program you may have installed from your PC today.