Background:
My in-laws have a conventional Highlander, which they love. They recently purchased a beach house, 300 miles away, and are making regular trips. I'm a Prius owner. I suggested they look into a HH, to help with their gas mileage. The dealer told them they would only see a 20% increase in MPG. My in-laws opted to not purchase a HH. Let's assume the dealer's an idiot, since that's not where I'm going with this thread.

This weekend, I drove my wife's 2002 automatic Passat wagon, full of people and luggage, to the beach. It gets an estimated 30MPG Highway. Using basic Prius techniques, I was able to get 31 MPG. If not for traffic and diaper-change stops, I'm sure I could have gotten more.

Question:
Are there any Prius drivers out there, with experience in a HH? What kind of MPG do you get? I have to think, using Prius hyper-mileage techniques, you could blow away the EPA estimates. I beat the EPA estimates, on a conventional automatic, with a full cargo load, and didn't try that hard.