I have that feature (called Sensor Reheat) on my microwave. It has a hygrometer and when it senses a good deal of steam, it thinks it's done. It works pretty darn well. It a medium setting so food's not burned on the edges and cold in the middle. That and the 'popcorn' button are my favorites.

-Zeke

Now if only they could make a self-cleaning microwave, that'd be something.