The site says the exterior changes are so minimal you probably wouldn't even notice the device was different than the iPad 2.
Here's how they described the new device...
The new iPad's body is so slightly thicker than the iPad 2 that the change is unnoticeable on first inspection; a roughly 1mm increase will barely be perceptible to users. We've heard that the only accessories that might have issues are cases, and then, only cases that were precisely contoured to fit the iPad 2's back. On the rear, the camera in the upper left corner has become bigger-noticeably so when placed alongside the iPad 2, but not so huge that anyone would think they were different at a distance. The new camera hole is silver-ringed, and does in fact look the same size as the iPhone 4S's much-improved rear camera system, minus the LED flash.
From the front, the site says the iPad looks the same. The side buttons and ports are all in the same location. iLounge says the changes are so modest that Apple could call the device the 'iPad 2S' or 'iPad 2HD'. They also got the impression that the device was more than half a year old.
That's not a huge surprise given how long pre-production takes for a "new" device, but a lot can change between mid-2011 and early 2012. All I can tell you is that every company I've asked about the next iPad seems to think what I've told you above is correct, apart from the possible screen size tweak, which remains uncertain.