Since my review of the 2010 Prius a couple of weeks ago, I have had a lot of questions come to me on the forums and in email about where the difference between the ECO and PWR (Power) lies during accelleration.  I contacted our friends at Toyota, and they provided me with a great slide from the media presentation showing the change in force output between the 2 different modes as you depress the accelerator (

In this YouTube video, Toyota's Dick Kelley gives tips on driving the 2010 Prius.  Not everything he says is 100% correct (EV mode is up to 25 mph, not 20 mph), but it's an interesting video to watch none-the-less.