The advantage of a tapered trailing edge is to reduce tip vortex and increase the time before laminar seperation. At least that's what I've been given to understand. I'm sure Brett will jump in and correct my technical misinformation. 
Paul said that the yaw problems he encountered with tapered trailing edges seemed to go away or at least be ameliorated with the use of a 4 stroke for power.
My new elliptical plane has a tapered trailing edge, elliptical taper AND diagonal ribs. The trick was to use StuntRib to design the ribs and plug the values into the spreadsheet. Worked fine, but was pretty tedious. And it makes for a somewhat thick TE in order to keep the aiirfoil and taper together and consistent. Should be an interesting wing. A hack of a lot more complicated than I had at first envisioned.
Randy Powell