There is a company that advertises in most of the sailing magazines that specializes in electric drive systems. Re-E-Power
. They claim that you can use it as a regenerative system while under sail, and a 4 year warranty.
As for the battery capacity of your boat, I don't see this as an issue. You said that you have a big honkin' generator. I am guessing that you want to use this as the power source, not the batteries. You would start the generator, as you would start the auxilliary on a regular boat, then use the throttle and transmission as you would normally. I beleive that Lepoard Catamarans use this same architecture with their electric versions.
I believe that the real benefit of such a system is that you are not as restricted about where the generator is placed on the boat, as you would be with a conventional (mechanical) drive train. If you wanted to put it in the sail locker to free up additional cabin space, you could. (I'm not saying that this is a good idea...)
That said, I agree with 'Hog and 'Dog that you would probably be better off spending those shrinking dollars elsewhere on your boat.
I suspect that the weakest link in the system is the drive control. Controlling all that current is going to require some heavy duty switches. Putting them in a high moistrure / humidity environment is askin' for corrosion problems. IIRC Lepoard has had some issues with their drive control software which is probably related to this humidity issue. (I think that there was a CW article on this last year).
Hope this helps!