More excellent advice Apple will no doubt opt to ignore; see the full post for more details and a link to download the full 93-page report
iPad apps are inconsistent and have low feature discoverability, with frequent user errors due to accidental gestures. An overly strong print metaphor and weird interaction styles cause further usability problems.
"It looks like a giant iPhone," is the first thing users say when asked to test an iPad. (Their second comment? "Wow, it's heavy.")
But from an interaction design perspective, an iPad user interface shouldn't be a scaled-up iPhone UI.