7CONIFIER lets you quickly alter icon sets in Windows 7
DeviantArt has a fairly active community of people tweaking and customizing Windows 7. One of their favorite tricks is to replace a whole bunch of system and software icons with desaturated or monochrome variants. This "unifies" the system visually, and the whole thing feels like one "package" instead of a bunch of disparate applications.
Usually, this is a manual process, and it's fairly laborious and error-prone. Not all icon sets supply icons for the same applications, and changing the files around can get old quite fast.
7CONIFIER is a slick application that makes this process as painless as possible. You feed it with an icon set, click Apply, and you're done. It's even responsible enough to propose creating a "default set" containing your current "vanilla" icons when you first fire it up.
To be honest, I'm not 100% sure it worked on my system. I mean, I see a different icon for Opera, but I don't see a different one for Notepad or for Explorer. So, I guess it's partially successful (at least on my rig). That's par for the course with this sort of thing – customization is tricky business!