Here's a speed vs MPG chart for the G1:
You can probably hit 55mpg even in an SUV if you drive slow enough. Drag goes up exponentially with speed (as I'm sure you already know).
Honda's IMA has a few advantages over Toyota's system. If the big battery dies for whatever reason, you don't get stuck on the side of the road. Lots of people drive G1's around with the big hybrid battery removed entirely, but it's not fun if you're using a CVT model. I also once had the ground on my engine kill switch fail, which cut power to my injectors. I was only a few miles home, so I mashed the pedal to the floor and managed to make it back on electricity alone in my G1.
You
can drive around in "EV mode" in Honda's later IMA hybrids, but the IMA is bolted to the engine's crankshaft, so you're still moving the pistons even if they're not firing. The valvetrain closes all of the valves so you're not pumping air though, so engine drag is greatly reduced.
On my G1 I have cruise control, bluetooth, HID projectors, a ~700w 4.1 sound system, and a trailer hitch. Next on my list of creature comforts are the seats - the stock ones were presumably designed with only weight reduction in mind.
