Most of these undoubtedly work but I always find that microwaved food tastes a little different. I would never use it as my sole method of cooking (some people do). Also, wouldn't it be quicker just to wait for the tap to run hot than microwaving a wet towel for a minute?

a lot of the projects above involve cooking on high for long-ish periods with very little material inside to soak up the microwaves. i suspect that over time, this could lead to damage to the high-voltage magnetron inside.

caveat emptor-- those things produce a pretty spectacular explosion when they rupture.