So I listen to music at work a bunch via headphones (here in Fargo, we've got cubes, not individual offices). I use my laptop as my "fluff" machine - that is, i listen to music, read mail, do office stuff, write up bugs, web surf (gasp!), etc from it.
Naturally, this doesn't have the "media" keys of the recently awful MS keyboards. So the common scenario is that a person comes over to talk to me and i have to find media player, restore it, hit pause, then take off my headphones, then turn to talk to the person.
What i wanted was a global "pause" button.
It turns out that somebody has made a tiny (12kb) program that lets you bind arbitrary key sequences (context-free, it seems) to arbitrary actions. This thing fits the bill exactly, and is available from http://dana.ucc.nau.edu/~tsr22/apps/hoekey.htm. It has stuff built-in to send messages to whatever app, so i can bind windowskey-P to send the play/pause command to WMP. Life is good.
As an aside, the default config includes "windowskey-4" as a command which..turns the currently selected window to half alpha-transparency.