I stumbled on the following microwave cleaning method this morning that's so ridiculously simple and so good I can't believe I hadn't known about this sooner:
To get out all the splatters and spots that end up caking the interior, fill a microwave-safe bowl with a cup of water and a few splashes of vinegar, or wedges of lemon or lime (which of course have the added benefit of smelling terrific). Zap it on high heat for a couple minutes until the water starts to boil and the window gets steamy. Wait 15 minutes for the bowl and water to cool, and for all that steam to penetrate the stains, before opening the door. Follow up by wiping down the interior walls and rubber door gasket with a clean cloth or sponge (and if the window is still grimy, use a half water/half vinegar solution to get it shiny). That's it-so easy, right? I just tried it and am deeply satisfied with the results, the fact that I didn't need to use any chemicals, and the whole process in general, which kind of feels like a grade school science experiment.