There was a fuel cell powered tractor in 1959 to show off this technology but progress has been slow.

From what I've read even the humble lead acid battery is currently far more efficient for energy storage.

More electricity would be need to produce hydrogen to power vehicles than electric vehicles powered by more conventional batteries. So from an electricity cost/greenhouse gas point of view it appears there are currently better alternatives than Hydrogen.

This was very disappointing to find out as this is not the picture painted by the popular (non-technical) press.
Despite this I would expect to see quite a lot more money thrown at Hydrogen powered vehicle research to try to over come these limitations.

Hydrogen vehicle - Wikipedia, the free encyclopedia
"Hydrogen fuel cells are theoretically more efficient than internal combustion engines, achieving efficiencies of 50-60%."

The Fuel cell entry in wikipedia also has some interesting information on this area.
Fuel cell - Wikipedia, the free encyclopedia