We'd like to put in a tankless water heater, for a number of reasons: it's environmentally sound, it will lower our electricity bill, and I'd like to be able to run a nice, hot full bath.

The problem is, we don't know anything about tankless water heaters: what to look for, what brands are good, or whether they're a bad idea.  So I'm throwing the question out to my ever-helpful readers.  Is this a good idea? And if so, how does one go about finding a good heater?