How Big Is Big Enough?

The crew at O'Reilly Answers recently posted an excerpt from Tapworthy about the ideal size of iPhone tap targets. Forty-four is the magic number:

Just how big is big enough when it comes to iPhone tap targets? Well, what's the size of a fingertip? Apple pegs it precisely at 44 pixels and this measure appears reliably throughout the standard iPhone controls. In portrait orientation, 44 pixels is the height of buttons in the Calculator app, of the keys of the iPhone's virtual keyboard...