Nothing. EXIF data is editable. MacRumors covered this bit a couple of weeks ago and concluded that it was probably authentic, although their logic escapes me. That story links to the source story at Mobileguerilla, where the basis for authenticity are the following:
The photo poster is allegedly an Apple employee.
The photos were posted and then removed.
The EXIF data lists the camera as an iPhone.
The photo was reported (by the poster) to have been taken at a Cupertino, CA restaurant three miles from the Apple campus.
Wouldn't win over a jury, but it does have an interesting whiff. But let the fantasy live on!
P.S. New request for iPhone 2.0: a white balance patch.