If you are using electric heat, chances are you don't live in a cold climate and pay for air conditioning for much of the year negating any "savings". Here in cold-balls Canada, EVERYONE has centeral heating; it's too expensive to use electricity. That being said, I do agree that datacenters' heat should be used to heat useful things (office bldgs, like you suggest).
You must be from the East. In BC, a significant portion of the province's electricity is generated by hydro power, making it very cheap. Most of the homes I've been in on Vancouver Island do not have central heating. Electric baseboard heaters are the norm. Because the climate is moderated by the ocean, it never gets atrociously cold, nor does it get extremely hot. I've never owned a car with A/C, and never needed anything more than a simple fan for cooling purposes. It rarely goes over 30 degrees in the summer for more than a day or two at a time. Quite pleasant, really.
I used to live in a tiny apartment above a garage, which contributed to it being freezing (relatively) in the winter. I would turn on my electric baseboard heaters for a short time in the morning, and my two linux servers, one XP box and one laptop would keep it toasty for the rest of the day.
