The Prius II seats are a huge improvement over the Prius I seats. I've got no back problems at all and the Prius I seats cause my back to hurt after more than an hour or so in the car. Prius II seats haven't caused me any problems so far, and they don't seem like they will as they have much more lower back support and better side to side support too. There are some good back support things that can strap on to car seats so they don't slide away for those with above-average sensitive backs that should be able to fix up the lack of technology in the seats. Also there's massage (vibration) and heating strap-on things that plug into the cigar-jack that may provide additional comfort and pain relief.

2001 Prius Photos       2005 Prius Photos
'97 Prius Simulation Prius inner workings