We actually went to check one out last weekend. As thehorsts and rickallen said his knees were right on the dash. In addition to being uncomfortable and dangerous in an accident, he was actually able to shift with his right knee. Bad news... to be zipping down the highway at 60 miles to the gallon, only to suddenly go into reverse and have your transmission drop out!

The dealership has called a mobility specialist (read: a company that retrofits cars for disabled drivers and passengers) to see if they could move the seat back. So far they've said it's not a technical issue. Apparently, the floor of a Prius is flat and the rails are attached to raised pieces that are then attached to the separately floor. They could easily detach the whole mechanism and move it back 3-4 inches. (Thehorsts point about the steering wheel extending is a good one though.)

They are checking with Toyota on whether or not moving the seat would negate the warrenty and/or if the airbag would still function properly. We're waiting to hear back on Toyota's answer and how much the retrofit would cost. I'll post here when we do.