I know I'm a bit of an oddity here (yeah yeah I know, spare me the obvious retorts) but I don't like food heated up in a microwave. Even left overs, I prefer to heat them up in a pan than zap 'em. Maybe a blind test would prove me to be talking through my arse but that's the way I feel.
At home we use the microwave to heat milk or to reheat a hot drink and to reheat boiled rice. Don't think thats enough use to justify having one on board.
Friends of ours who have one on their Beneteau 50 and they reckon it makes a great bread bin.
“Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life.” Terry Pratchett