I have had my Prius more than 5 months now but I just went on a 200 mile drive today with 2 other passengers...and let one of them drive part of the time (because the arm-twisting was too much to bear) so I got more experience as a back-seat passenger. A few things I noticed:
(1) The back seat legroom is really quite amazing. Admittedly, I am fairly short and so were my fellow occupants. But, just comparing it to other cars...I was in the backseat of a Subaru Outback on a Labor Day trip and today's experience only confirmed what I told those Outback owners at the time, namely that their car simply does not have the backseat legroom of my Prius. I don't even think it is particularly close.
(2) I had a couple more opportunities to pass on a 2-lane road (which have been infrequent because of where I've driven over the last 5 months) and I am always amazed at how much zip it has to pass. (Admittedly, my last car to compare with was no hot-rod...It was a Plymouth Colt, but it did have a manual transmission which I thought gave it at least decent passing acceleration. But, the Prius is clearly better.)