Its pretty seamless when the gas engine cuts out and the electric motor takes over. If the stereo is on, Its hard to notice. Its a weird feeling at first looking at your gauge cluster and seeing zero oil pressure, though!
I've got 6k miles on mine. I commute 62 miles per day with some hilly terrain and steep grade. I average 26MPG. I have found that gas plays a huge part on mileage - I've consistently gotten my best mileage using ethanol free 93 octane.