We converted this past year to "Geothermal" (VERY good point, Mark). It's essentially a large refrigeration unit that runs the refrigreant compression/expansion cycle forward for summer cooling and reversed for winter heating. It's a matter of a reversing valve.
Five ton unit, five looped wells drilled to 180'. We live in an area surrounded by lakes so they hit the water table 20' down which translates to HUGE heat transfer efficiencies.
Now, we haven't had a winter of heating yet, but our gas bills were ~$400 per month from November through March.
With the system running in summer mode, it blew VERY cold air and kept the place @ 78F all the time which was super comfortable.
The cost was all electrical (mostly for running the compressor, some for running the ground loop) and ran ~$145 for the months of June, July, & Aug. Previous year costs were about $120 per month for the cooling season.
We have radiant floor heating in the first floor and the refinished basement & forced air for the first, second, & finished attic.
It's going to take some 'tweaking' with the various thermostats and the Clydesdale to keep the forced air from running... Hopefully, we'll just have the radiant heat going most of the time & have the forced air kick in when I'm not around to stoke the insert.
Hopefully, the cost of heating will be in the $140 - $150 range or my wife & I are going to feel like a couple of fools for spending so much $$ on converting our old HVAC to this new one.
Another caveat: If the Democrat's Cap & Trade legislation goes through, our electric bill is going to go through the roof... Most power generated in the North-Central US is done with Coal... evil coal...
I have half-a-mind to send more good money after bad here and get a 50KW photo-voltaic system put on the roof and then tell the power company to come and take their meters off my building.