They couldn't find anything wrong with my Prius. However, I *did* find out that I'm supposed to be using low octane fuel. Apparently, they use higher levels of alcohol to achieve high octane gasoline (in Colorado anyway), and that's not good for the engine.
I'm somewhat annoyed, as this fact is not in the owner's manual and I have no idea what long term effects this will have on my engine. Guess I better trade it in before I find out, eh?