Don't give up yet. I just passed 1000 miles and gassed up for the 3rd time. Second tank averaged just under 26 mpg - both computer and manual calc. I reset the computer after the that fillup. This last tank was even better. The trip computer calculated 27.9 mpg. My calculation of fuel consumed showed an even better 28.75. I would estimate 70/30 highway/city driving.
My electrics shut off quickly too when starting from a stop. However, I have noticed that the worst mileage is the first outing of the day or whenever the engine is cold or the batteries are not charged - not sure which is really causing the issue. This past week, I have been driving a relatively short 5 miles one way. The car sits all day, and then I make the return 5 mile trip in the evening. I am doing well to average 24 mpg in all slow, city driving. About the time I am ending my trip, I start to see the electrics begin to perform a little longer. Others have posted this same issue. There is a "warm-up" period during which the mileage suffers. If the 400h is going to be used consistently for very short hauls, there may be difficulty in achieving predicted mpg levels. Otherwise, be patient, the mpg will come.
Enjoy.