I tried Pie Guy on my iPhone 3GS. My initial reaction was there was a bit of a lag in controls. Enough that it made it hard to control. So I deleted it. Impressive use of cutting edge web standards technology. But I can’t see it as anything more than a tech demo.
The only reason I mention this is because (a) a web app isn’t going to compete with a native iPhone app for a game, and (b) web standards technology is still a ways away from matching what Flash can do when it comes to interactivity.