Well, back before the second-gen (2004) model came out, and had huge demand because of Motor Trend, I test drove a 2002, and at the time was told there would be a couple month wait, since at the time, you really ordered it from Toyota, not purchasing one from the dealer. The dealer had a used one on the lot for $1000 more than MSRP of a new one. When I pointed out the rediculousness of it, he said simply "this one is more because you can drive it off the lot now."
With the frenzy over the 2004 model, that only increased. I bought mine for $5000 over MSRP (sorry, I don't feel guilty. It was either that, a 9-12 month wait, or buy it out of state, which I didn't have the time or energy to do.) The same dealership had a used fleet model (white, NO package, not even the rear wiper,) with over 10,000 miles that they were selling for $28,000. I called back a few weeks later, and it had indeed sold for $28k.
I haven't heard of any private-party sales for more than MSRP, though. (Mostly because Prii are so prized in Portland that nobody wants to sell theirs!)