I believe MacRumors when they report the resolution as being 2048x1536. That's what they were told and they reported it faithfully. But I can also see how they might have been scammed.
Did you catch the Quora thread 6 months back that explained how Apple stays ahead of the competition? Let me summarize it. Apple gets the cutting edge tech first because they also provide at least some of the capital costs to build the factories. Apple gets the exclusive as part of the deal.
Now, if Apple has an exclusive on this new hi-res screen, what are the chances that the screen would show up in a parts warehouse? I'd rate it as somewhere between slim and none. Apple is simply fanatical about preventing leaks. There's no way that a parts supplier would risk Apple's displeasure by letting one of these screens out in to the wild.
And yes, MacRumors posted a close up shot of the screen. The photo shows what looks to be some very tightly packed pixels. But will the screen actually work, and will it really show the higher resolution? We cannot know for sure until someone powers it up, and we cannot power it up without the appropriate the drivers and controller chips. So for all we know this could be a scam from some back alley parts maker.
While I do believe that the iPad 3 will have the new higher res screen, I don't think this particular screen is actually from an iPad 3 production line.
What do you think?