A few thoughts on comments here:
More diesels are being introduced in the US. I think there are some companies trying to get them going again. The issues at least around here is that while you get 20-30% more mpg, diesel costs sometimes 30-40% more. It's a weird tradeoff. Maybe as we get more biodiesel of some form this will change.
Charging the Prius batteries. If it's really low, the engine will run more to charge the hybrid batteries, and I'm sure that dealerships deal with this issue. They might have cars sitting for months, and in cold weather, the hybrid can run down. But it charges as you drive, so I don't think there's a need to idle them up. might be a sales tactic (and a poor one) to get the battery reading in the green rather than the blue (mid) or purple (low).
2010 is supposed to see a plug in Prius come (and maybe some others). I've had my Prius idle for 2 weeks, we start it up and the hybrid is low, but it charges right up as we drive.
Hypermiling - I've tried it a bit. It gets hard to do in places in CO with the hills. Especially when other drivers don't want to hypermile with you! 😛 I worked a tank at the end of the summer, some mixed city/highway that was longer trips (couple hours) and had about 400 miles into a tank at 57mpg. Blew it back down to 55 with a few errands at the end of the tank, but got to about 535 mi on 9.xx gal of gas.
Batteries - I've read a bunch of conflicting reports on this. There are definitely things done with mining batteries that we might pay for later with the heavy metals. No idea if its' worse than computers and their circuit boards or a lot other stuff humans build. However Toyota has tried to really make these recycleable in a lot of ways. They offer payments for recycling and they've done design work to try and reduce the environmental impact of the the car overall. There's no lead in the battery, either. That Hummer v Prius article has been debunked fairly well as a sensationalistic piece.
The car definitely does better in the city. Sustained 70mph rides result in lower (40-45mpg) mileage than stop and go in the city. However constant acceleration really kills mileage as well. you want sustained speeds, 40mph seems to be a sweet spot, where you can get 80-90 mpg.
My drive from home to the grocery store is hilly, 10mi, but falling 4-500 ft in altitude. I can average 80mpg on that drive, which is mostly 40mph. The return trip drops to about 40mpg, mostly on the couple large climbs that go up 3-400 ft.