I drove some kind of rental car with one a couple years ago, Dodge Caliber I believe. I hated it the whole time. There was no reasonable way to accelerate once at cruising speed. If you rolled on throttle, it would change the gearing so that the rpms went up, but it didn't actually accelerate. You had to go to about 3/4 throttle before it would start to actually pull, and then that would put you at 5k rpms. Also, it felt very laggy and was weird, but those are probably things you get used to. All in all I couldn't stand it.
With that said, I've got a 95 Polaris ATV that uses the same concept for the transmission, and it is fantastic. But the throttle to acceleration relationship is much better. I believe the execution has as much to do with it as the type of transmission.