I know there are units made which are supposed to be sized for use in a residential kitchen, as a more efficient replacement for the usual vent hood (bring air in to replace air blown out, but transfer heat between the two so you don't lose as much heating/cooling as you would with a normal just-blow-outward setup). I like the idea, but they ARE more expensive (of course; two fans and the heat exchanger and the internal ductwork to feed it) and I'm not sure how much maintenance they need... especially since in a kitchen setting you're going to get airborne grease and so on which may make keeping it working efficiently difficult.
So: If you've installed one of these, how did it work out and would you do it again?