Ok, so the FAR is online and I don't have to buy it.
As usual, when dealing with gov't regulations, this is as clear as mud.
Reading 61.5, the multiengine RATING is required to operate aircraft with more than one engine.
Reading 61.31, additional TRAINING is required for operating complex, high performance, pressurized, or tailwheel aircraft.
61.31(k)(2)(iii)(B) gives exception for the RATING requirements when the aircraft is operated under an experimental certificate, UNLESS a passenger is being carried.
So, if I'm reading this correctly (Chris Barber can chime in anytime), Wayne is correct that an experimental multiengine aircraft can be flown by a non-multi engine rated pilot, provided he/she is the only person in the aircraft. However, no exception is given for the training requirements for complex, high performance, pressurized, tail wheel, etc., because these are not ratings.
It also doesn't give an exception for the pilot CERTIFICATE or the medical CERTIFICATE requirement, so you still have to be a certificated pilot, and have a current medical.
I am still fuzzy on the turbine or >12500 pound issue, but since that is a type RATING, I'm thinking the RATING exception covers it also. I can't afford to put gas in a turbine, and I don't think I want to sand 12500 pounds of fiberglass so I'll let Greg worry about that one!
Does this make sense? Since when did the gov't ever have to make sense?