iPhone Central's Christopher Breen describes his experiences with a an early version of a racing game for the iPhone:
While standing in the Developer’s line an acquaintance of mine took the time to whip out his iPhone and show me a racing game his company was working on. The graphics were glorious, the accelerometer controls were extremely responsive, and the results, in my case, were absolutely nauseating.
Of course, Breen admits that in the past he's looked down on those who would complain about people complaining about the motion-sickness caused by 1st person shooters, labeling them weaklings.
Of course, the BBC's Maggie Shiels had a better time of it describing being "hooked" by Super Monkey Ball:
The graphics are really clear and bright and the movement of my monkey was dynamic. Tilting the phone to move my character was my downfall. I just wasn't very good at it.