Sort of on topic here, I had an opportunity today to compare fuel economy with the engine cold vs warmed up. Reason: I forgot my keys and phone at home.
Anyway, on a cold day my 5.5 mile drive to work usually results in about 22-23 MPG. The engine reaches normal operating temp about halfway through. Before I left for work for the second time (with the car now fully warmed up) I reset the SGII, and then checked it when I got to work. Result: 27 MPG. A rough calculation says that a $33 block heater would pay for itself in two years, at current fuel prices. Although that assumes a fully warmed up car, and from what I've read this only gets the coolant up to around 150*F. But throw in the comfort factor and the reduced CO2 output and it's a no brainer.