The iPhone 3.2 SDK for iPad has officially outs the PowerVR SGX as the graphics core inside Apple's A4 chipset:
Using OpenGL ES on iPad is identical to using OpenGL ES on other iPhone OS devices. An iPad is a PowerVR SGX device and supports the same basic capabilities as other SGX devices. However, because the processor, memory architecture, and screen dimensions are different for iPad, you should always test your code on an iPad device before shipping to ensure performance meets your requirements.
Since Apple is a major stakeholder in PowerVR creator, Imagination, this was widely assumed, Bright Side of the News had suggested otherwise.
Whether or not it's the same PowerVR SGX in the current iPhone 3GS, or the latest generation announced back in January at CES remains unknown. We're hoping for the latter, of course, and that the 4th generation iPhone gets it as well...