I thought that the distinguishing feature of munchkinry is that it's an ingenious solution which cannot be effectively reused, and thus its main utility is inspirational. Like the Kobayashi Maru test hacking, or winning a Game Room battle by rushing the gate, or, in less fictional cases, using airplanes as powerful incendiary projectiles, or winning over $100k by gaming a game show.
Some people use the term that way, but at least in the pen and paper roleplaying world it is closer to how D_Malik is using the term.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.