Fuel cells may be a promising source of energy for cruisers. Engadget has an article about Samsung's DMFC (Direct Methanol Fuel Cell) that is set for release to the military next year. A 3.5 kilo (7.7 pound) brick will supply 1800 watts. This is enough to run a military laptop and other gear for three days without recharge.
1800 watts is also about the three day output of my modest solar panel installation. It is easy to imagine a slightly larger unit supplying power for a week or two during an offshore passage. There is also the potential to recharge the methanol from a small day tank.
You can find background and technical information on DMFCs here and here.