best way to clean microwave:
The best way to clean a crud ridden microwave is to wet down a COTTON dish towel until it's almost dripping, put it in the microwave and run it on high for 4 minutes and leave it alone for about 10 minutes without opening the door. (no it won't catch on fire or hurt the towel either)
Remove the hot wet cloth carefully, then wipe down the whole inside with the wet towel followed by a clean dry cloth. You may have to let the hot cloth cool off a minute or two. You can squirt a little dish soap on the wet cloth if you want to cut through the grease.
This works like a charm no matter how dirty your microwave is!