So here's a crazy thought.
I wonder if it's possible to configure a rig so it's like an appliance...the goal is basically to have it be a space heater during winter...which also churns out bitcoins occasionally.
I kind of have a setup like this. I have 5x of the ButterflyLabs 60GH/s ASIC miners mining Bitcoins. Each of them is roughly the size of a small space heater or shoebox (say, 5"x5"x10"), they have fans taking air in one side and exhausting it out the other side. Unfortunately, the power and USB ports are on one of the long sides, and these cables have long connectors and are not very bendy, so it is not possible to get them very densely packed. Furthermore, the requirement of an external power supply has its limitations. This is what they look like (5th unit out of frame):
However, after that photo was taken, I reversed the fans on 2 of the units, so I was able to push the 4 units together in a rough cube, with all 4 taking in cold air from one side, and exhausting heated air out the other side. This is roughly 1000W of hashing power in roughly a 10"x10"x10" cube, with 4x 120mm intake fans and 4x 120mm exhaust fans. I have it sitting on a desk in an otherwise empty studio apartment, with the A/C turned to keep it cool when necessary, but the mining units will provide enough heat to keep the apartment fairly warm in cold weather. They are pretty loud, definitely louder and more unpleasant sounding than most space heaters. (92mm fans inside on the heatsinks = higher pitch than the 120mm fans on the ends. IMO their engineers failed at airflow, they should have just gone with full-height heatsinks, oriented the right way to allow the 120mm fans to cool them.)
I will note that even with 1000W being dissipated, the exhaust does not get super hot like an actual space heater does. It is more lukewarm. This is not too surprising when you consider that most actual space heaters produce something like 1500W out of roughly 1/4 the size.
The 300GH/s from my 5 units currently produces roughly 0.048 BTC per day.
I also had a Butterfly Labs Jalapeno unit. It produced 5GH/s and was pretty quiet. It looked nice and could sit beside my laptop on my desk. It got warm enough to warm my hands when they got cold. I sold it on eBay, but I will probably buy another one in a year's time when they are worth pennies, just for novelty.