If you haven't yet, go read HobbesIsReal's great How To: Edit the Registry. He ends the article with some suggestions as to where to find some useful registry hacks. Here's one I've never heard of that's super cool: you can set up your bluetooth headset button to launch whatever voice recognition application you prefer -- or heck, set it up to launch anything at all:

For users of bluetooth headsets, you might face either or both these problems:

When you press the button for voice command on your headset, the default program (Voice Commander) comes out but you want to change it to something else.
Pressing the same button, nothing happens.
If this sounds like you, then there’s a very easy solution for you in the form of a registry hack

Head on over to Eten Blog for the full details on how to make the registry edits - there's even a “.reg” file that you can use to add the keys to your phone and “import” them into your registry (if that's your thing).

That's what's cool about the registry, the neat hackable things buried in there never seem to end. Yeah, a registry is sometimes not the best option for computing -- on a desktop, for example, I much prefer the Mac method of discrete text-based pref files to the Windows Registry. Windows Mobile, on the other hand, has less complexity than XP or Vista so a single database of settings makes a lot of sense.