Just fitted out an IPAD3 with an Otterbox defender case and thought I would share some opinions.
the case itself is made of three major components. the cover which doubles as a stand, the silicone jacket and the polycarbonate case. assembly was straightforward and fit of the iPad 3 in the ipad 2 case was good, but lets get down to the form and function.
Bulk: Well its almost not a portable device any longer, the case is bulky in fact too bulky. Once you remove the stand/cover its a bit better but then unless you clip the cover on the back you have to find someplace to put it and this adds one layer of inconvenience. the iPad 3 becomes over an inch thick and heavy too. It just does not slide into a bag easily any more. be nice to have some sort of thin fold down cover. By the way, the magnets do not shut off the iPad.
Protection: against shocks, very good, dust- poor water/moisture none
The drop protection is good, minor bumps and bings in a boat were well absorbed, however dust entered every port and soon permeated the case. Poorly protected area were the speaker which is completely unprotected, the microphone, and both the rear and front cameras. All almost seem to attract dust which seemed to distribute well through the case. After two days on dusty roads I had to take everything apart and clean it with the speaker taking the worst hit.
Moisture: Otterbox clearly states that this is not a waterproof or water resistant box. They speak the truth. I tested it empty and after one hour at the helm of a boat an iPad would have been toast. Worse still any rain would have been fatal for the iPad.
Function: the bulk is an issue and it is heavy, the cover only one position as a stand and otherwise a lot of bulk for what it does and..... you need some place to put
Overall its bulky shock protection and little more. I have had otter boxes for an iPhone as well and had the same issues. If you are looking for waterproof and rustproof try LIFEPROOF boxes which have their own unique problems but give similar shock protection but total water and dust protection. The iPad 3 version of this case are not out yet but their iPhone cases are top notch.