There is always more and more claims of greater fuel efficiency at higher speeds, etc. This is probably true in any motor powered endeavor, be it boat, airplane, car or spaceship.
Malcolm Tennant is a professional catamaran designer (check out Tennant Design’s home page) who is an active contributer on the Power Catamaran mailing list. Recently he pointed to an article (Escape Fuel Consumption) on his web site that has been there a bit, but shows a nice graph and interesting writeup detailing fuel usage of some different hull designs at different speeds. Obviously I can’t vouch for the data, and the tests were done examining certain hulls.
What I found most interesting was the very obvious "bump" in the graphs for different hull types as they reached hull speed/planing speed. This showed me graphically in a way that reading words doesn’t always make clear just what you are overcoming to "get on plane" or when reaching hull speed on a displacement craft.