InformationWeek reports that an empty slot on the iPad could actually be for the digital gyroscop, based on a teardown by UBM TechInsights.
TechInsight’s senior analyst Steve Bitton speculated that the iPad will likely get the gyroscope for a number of reasons. First, the presence of the slot (see images) leads to the obvious conclusion. Moreover, the accelerometer and gyro would likely work together, as well as with the application processor (the processor right above those other two components). Thus having all closely co-located makes sense.
Source: InformationWeek

“So where have the news, opinion and analysis taken us so far? Can we say that the A4 is truly differentiating hardware, or is it more of an evolution of those that came before it?” -EETims has a thorogh analysis –  Read all about A4 here