So I tried to crank down the central heating this year at night to around 55 & put an electric heater in each bedroom. Here is what happened:
For January-March I broke even on gas. The average temp for 2009 & 10 was exactly the same 29 degrees and I averaged the same gas usage 114 therms.
Electric for 2009 cost us $65 on average a month.
Electric for 2010 cost us $89 average a month because we used A LOT more electric.
Results- electric room heaters may be worth it in a drafty room, but it cost more to crank down the heat at night & use electrical room heaters.