The question is: How do you clean the microwave?
You have to put food in there, so bleach products and ammonia are out. You want an ammonia-flavored Hot Pocket? It's an electronic product, so scouring powders are a bad idea. Oven cleaner? Not made for microwave ovens.
You need an angry mama.
The Angry Mama Microwave Cleaner arrived at Christmas, and is a handy little gizmo. It works by the same principle I've always used, that of nuking up a bowl of water really hot and letting the steam loosen the gunk on the oven interior. Some elbow grease does the rest.
The problem with this method is one I found out the first time I tried it -- superheated water is dangerous. The FDA reports "serious skin burns or scalding injuries around people's hands and faces as a result of hot water erupting out of a cup after it had been over-heated in a microwave oven. Over-heating of water in a cup can result in superheated water (past its boiling temperature) without appearing to boil." I did not get burned, fortunately, but here's what happened: I put in a bowl of water with some lemon juice and set the timer to Kill; when it was done I opened the door. "If superheating has occurred, a slight disturbance or movement such as picking up the cup, or pouring in a spoon full of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup," says Mr. FDA, and opening the door was enough. BANG!
The Mythbusters did a nice demo on this years ago:
After my escapade I adapted my method by superheating the water and then leaving the bowl in the microwave until it had cooled off, 10 minutes or so.
You still have to do this with Angry Mama. Since Mama is plastic, she seems to require less time to get past the explosive state (instructions say to wait two minutes after nuking before lifting), and she has those stay-cool arms for safe removal. The manufacturer recommends a mixture of vinegar and water rather than lemon juice. You'll still have to use some muscle to scrub the inside of the oven -- those cheesy splats bake on like concrete -- but the job is far easier. For one thing, she has steam holes in the head to blast steam at the ick that forms on the microwave roof. When the job is done, she's ready for a bath in the dishwasher.
So we're glad we got the Angry Mama, and recommend her. Better and safer than the old bowl method. But she never does stop looking mad. I guess she's seen the state of the refrigerator.