I agree with Ryan 100 percent. I experience problems with zero-margin design when I try to scroll a list but it registers as a tap. To compensate, I have to be super careful when scrolling and not lift too quickly.

Now, if your device + app is really good at managing multi-touch events, then it is less of a problem. Zero-margin design can work. But margins literally provide margin for error, if your chosen interface has to do more than tap to get stuff done.