I've just passed 4,300 miles and I can definitely state that the 3,500 mile barrier several folks have mentioned does exist. Once you hit 3,500 miles, MPG does improve. I don't know if it's coincidence... because of summer temperatures, or just because it takes 3,500 miles to get comfortable with how to drive this car efficiently.

I filled up yesterday and my calculated MPG came in at 54.7. I've got 57 miles on my new tank now and I'm up around 59... that's driving around 60 mph with light A/C use and one passenger. Best numbers I've ever seen! Next tank I'll be getting my "hypermiler" star in the database for sure!