I'm going to make some custom light fittings for my Dad's old boat, which after 6 years is almost ready to be seaworthy. All the old fittings in the cabin are incandescent (plus a couple of 12v florescent strips). I'm going to replace all the spots, and add some downlighters, all based on LED technology. The florescents, we'll keep.
Browsing Farnell, I've found Luxeon LEDs that now achieve 100 lumens per watt (100 lumens output, 3.5v forward voltage, at 350mA). These LEDs can be driven to a maximum of 1 amp. The efficiency drops off as you increase the current (when running them at 700mA, they have an efficiency of 75 lumens/watt, giving something like 180 lumens). What's more I have some similar Luxeons from last year with the Lambertian lens and they give a nice, spot-free wide angle illumination (the ones I have already are red, though).
I'm going to build a custom power supply for each LED - there's quite a range of high efficiency buck converters specifically designed for LED power illuminators. The power supply should be pretty small, I think the PCB should be about the size of a postage stamp (all bar the inductor will be surface mount). The driver IC has a control pin, so it'll be trivial to make the lights dimmable. The LED driver can achieve 95% efficiency, too.
The biggest issue will be thermal dissipation - there's not much room to dissipate the heat the LED generates in the small amount of roof depth, so it may be simply best to use a fairly large sheet of aluminium to keep the LED cool enough.
Who says lights are boring? This sort of thing gives the opportunity for much tinkering!