I'm sure its not the only place but these kinds of efficiency issues have been debated for a couple years on the Prius sites, like priusonline.com and priuschat.com. There's some real world evidence and data to back up alot of these things, mostly because the Prius comes standard with a screen that estimates your mpg every 5 minutes of travel, and a dynamic read out that gives you a sense of fuel consumption every 10-15 seconds. You obviously use more fuel heading moderately uphill, but its kinda amazing how little fuel you can use heading downhill or on low uphill slopes. So a few conclusions I can draw from my own driving habits since 2002 driving 2 Priuses:

- tire inflation is good; proper at least, a bit above that for a 2-5 mpg bump (but never exceeding the maximum psi); you have to check this often and keep the right inflation to benefit, and you should invest in a tire gauge that gives an accurate readout too, not one of those little stick gauges
- low rolling resistance (LRR) tire models are good, replacing the stock tires with a better brand were worth a couple more mpg in my case anyway; they don't necessarily wear out any quicker, my current set are a 40,000 mile brand, but they aren't great in all conditions, so shop carefully and reward the vendors with the safe, long-lasting tires on conditions that you drive
- changing or cleaning your engine air filter is good, its like your lungs, you want the right amount of good clean air for proper combustion
- changing oil is good, my mpg always bumps up 2 mpg after
- as is keeping up on general maintenance, particularly tire alignment, there aren't too many pigeon-toed four minute milers and the same goes for your car
- AC makes no difference, in fact on the Prius folks report better mileage with the AC set to On; I've never noticed any mpg difference with AC on or off so usually just leave it on
- hypermilers aside, *in a Prius* a quick start isn't penalized as much as in other cars, owing to the high torque and assist from the electric motor; getting up to your cruising speed quickly lets the engine cruise longer; anyone's mpg may suffer in stop and go traffic, but at least with a Prius when the traffic stops so does your gas engine; outside a hybrid ymmv literally
- hypermiling really does work in the Prius anyway, but fwiw its such an annoying way to drive alot of folks forego it and just live with their 45-50 mpg. Thanks to the interweb I'm now stuck behind Cadillac Escalade's trying to emulate the Prius hypermilers, all so they can get 12 mpg; and there's nothing worse than those Prius owners bragging about 70 mpg, they drive like little old ladies (with apologies to little old ladies anywhere, they are sweet, bragging Prius owners are not)
- lowering your speed really helps, 60 mph seems a pretty good speed to go, 70 mph and you give away alot of mpg in a Prius, although I still get about 45 mpg on 200 mile round trips heading up and over Snoqualmie Pass along I-90.