Jon Simpson
The A4 and the A8: secrets of the iPad's brain
Piece from Ars Technica about the Apple A4 chip in the iPad, with speculation/informed guesswork.
the A4 is a 1GHz custom SoC with a single Cortex A8 core and a PowerVR SGX GPU
The author seems to attribute the quiet on Apple’s part about the architecture to the fact that its a relatively mundane part - I think it’s more in line with their general strategy of worrying about what things do, not how they are achieved.