My experience with the Lexus GS 450h, although brief, has been overwhelmingly positive, both in terms of performance and mileage. I drive 500+ miles a week; 80% highway, 20% city. I have consistently been averaging 28+ mpg highway (150 + mile trips), 27+ mpg city (5-15 mile trips). Having the minute-to-minute feedback from the gas consumption screen enables you to maximize your mpg, and once you learn the correct way to drive a hybrid, the fuel economy is certainly attainable, if not beatable! And that includes a mixture of usual gas-hungry aggressive driving such as frequent quick accelerations such as merging from an entrance ramp, and just blowing away fellow drivers when passing.
Acceleration, navigation system, audio system. Mpg with responsibility and fun.
Integration with Sirius satellite radio, which I hear is forthcoming.