I used my block heater this morning, first time since last winter. It's only good for about 50-60°F over ambient, which was 38°F this morning, but it was enough of a head start that my radiator fan cycled once as I approached work. I probably should have left one of the squares off.
Averaged almost 23 MPG, where any drive in over 20 MPG is a good trip. (Drive home is almost always higher since it's warmer by then.)
These things work!