Commercial natural gas electrical generation facilities are about 35% efficient. It is probably inappropriate to consider transmission losses since natural gas power plants tend to be located in areas of high consumption, but that 35% only goes down on the way to the end user. Remember, it doesn't have to beat the utilities for it to make sense.
Consider a house with a $200/month natural gas bill for heating. At $1/therm that is 200 therms of gas. Let's just guess at around 10% efficient for these cells, 220 therms of gas would give us our 200 therms of heat plus 20 therms of electricity which we convert to kilowatt hours, about 600 kilowatt hours. At $0.12 per kwHr that gets us about $72 of electricity for $20 in gas. Let's just say for every $3 we currently spend on gas we can get $1 of 100% efficiently generated electricity (1/3 the carbon footprint).
At 37°N, in December it would cover half of my electricity for a free standing house (but remember I made up their efficiency. At 20% it would cover all of my electricity. Googling about shows a record high around 60% and some press releases around 50%. I have no idea what these are, but it is probably several times the 10% number I used.)
During summer when I'm using nearly twice the electricity my gas bill is so close to zero as to not matter.