From Appletell's review of the GameHandle for iPhone and iPod Touch:
"As much as Apple wants you to think the iPhone and iPod touch are gaming devices, the fact remains that they're simply not built that way. The screen? Yes. The processor? I suppose. The input and ergonomics? No, no, no, a thousand times no. They aren't comfortable to hold, and the lack of any physical buttons for input makes controlling many of the games an exercise in frustration.
At this point, I'm convinced there'll never be an adequate iDevice input attachment for games, so we're permanently stuck with virtual d-pads and accelerometer controls where they shouldn't exist. However, Tunewear has addressed the comfort issue - imperfectly but efficiently - with the GameHandle."