It's a style of driving that can get your average MPG up. Some of it is very easy and doable for any make or model (diving at ideal speeds, avoiding hard breaking; drving long enough distances to overcome start up fuel wastes.) Some of it is geared towards the Prius (coasting so that you're not using the engine OR the regenerative braking; getting up to speed with the pedal depressed just enough so that you spend a longer period of time at the ideal speed/higher mileage without wasting too much gas trying to race off the line.)
Some of it dangerous, though it most often invloves down hill speeds that are too high (drafting is a hyper miller no-no, you're likly to have to *gasp* touch the breaks!), some of it is uncomfortable (no air on and windows up), and almost all of it requires paying attention so that you're doing the most gas effcient thing for your car, location, and situation.