I can't think of the names of any projects right now, but I have seen it done before, and yes, it works. You get down to a certain depth, you're past the frost line, you're into a fairly stable temperature regime, and it would be good. I think geothermal is the second-best option, though. What you're trying to do is recreate the ability to be underground. You're above ground, which is where a lot of people want to be. You're just drawing the heat that's underground up, and you're circulating that through the building system and through the district energy systems, and then putting it back down.
On April 2nd, 2009. See this statement in context.