The original iPad I received from the first Saturday shipments had some dead pixels so I had it swapped at my local Apple Store for one of the 'service' units in the brown boxes. They assured me it was new and not a refurb or other returned unit. The Geniuses were not real familiar with that whole process (yet) but swapped it nonetheless. The first unit never froze at all doing anything, including video playback of all kinds, including those listed below.
The replacement unit constantly freezes when playing back video from many sources. ABC player is the worst. It will freeze, or cause the iPad to spontaneously restart. I record OTA HD TV shows with Elgato EyeTV on my iMac and encode for iPhone and sync these to the iPad via iTunes. These H.264 videos freeze. I share AppleTV resolution H.264 EyeTV shows via web sharing on my Mac Pro and access these through the iPad's Safari browser. These H.264 videos freeze. All of the same files that freeze the iPad never freeze my iPhone, Macs or AppleTV.
So, content resident on the iPad freezes, along with web content streamed via wifi from my TimeCapsule on a very fast cable internet connection (20gb+ downstream.) I monitor the Time Capsule's wifi logs and see no issues except that the iPad reconnects after each crash and hard reset. The only way to recover from this issue is to hard reset holding the home and standby buttons.
So, my not-so-scientific testing and monitoring shows that the second service unit I received is probably no good, but the first one with the dead pixels was fine.
I decided to call Apple Support (I have AppleCare on this iPad and all of my equipment) and open a case. I got a call back as promised at exactly the time scheduled and a very competent rep had me reset my settings after spending a good 30 minutes on the phone trying to get it to freeze again, but it did not. I didn't try ABC TV but should have while on the phone with him. We agreed to monitor the situation and we'd check in with each other in a couple of days and I would call back if the problem persisted. It still persists. I left him a message and he'll get back to me.
My problem is that if I return it again for a new unit, what are the chances that the new one will also be bad?? Until Apple identifies the issue and can stock known, good units, I don't want to keep swapping iPads. Though having the bad units to test will help Apple find a resolution for the problem.