The registry cleaning portion is questionable, I haven't noticed any improvement after using it but no failures either. I've come to the conclusion that the registry cleaner does little or nothing beneficial.
Knowing your surfing habits and your profession I'm not surprised. You shouldn't notice any improvement, at least not on your personal computer. My customers have been very happy after I've cleaned their computers with CCleaner, so apparently it works. Furthermore, there was an article by Fred Langa in WindowsSecrets.com where he tested whether registry cleaning would do any good in Windows 7 or not. He clocked the startup of a lean clean computer, then he installed some well known "potentially unwanted programs", clocked again to notice the boot time had increased by minutes. Then he uninstalled the said PUP's the normal way, noticing the boot time was still over double to the original. CCleaner and a couple of other reputable registry cleaners normalized the boot time.
Of course you can dispute the testing method, but in my opinion if several cleaners all give similar results there must be a noticeable improvement. And as you said, no failures either. In my eyes that's a good attribute for any program.
