Go check out Ballard Corporation and see what you can find. From what I've read, they use a catalyst to split the hydrogen from the hydrocarbon. That hydrogen is then used directly in the fuel cell to generate electricity. It appears to be very efficient, certainly more efficient than burning it in a car engine. Right now, the sticking points appear to be the costs of the catalysts and developing fuel cells that are compact and light enough for automobile use. Since 746 watts equals 1 horsepower (at 100% efficiency), you'd need a fuel cell that can produce somewhere around 100 kilowatts to power a car. They've done it with hydrogen fuel cells and are working on it for the other fuels.

Ballard and other companies have developed domestic fuel cells for home use. These are typically fueled by natural gas and can produce around 5 KW. They don't have the size constraints of an auto fuel cell to worry about nor do they produce as much electricity. They seem to be about the size of an air conditioner. I'd love to see the cost per kilowatt/hour figures for these devices.

Ballard has also developed a small fuel cell for domestic electricity production in Japan. It's a small device built to produce about 1 kilowatt of electricity from natural gas. It's designed for inexpensive supplemental electricity during peak loads. I don't know how efficient this would be compared to a conventional steam power plant but it might cost less per kilowatt/hour than a gas turbine.