The iPad 2 is "about half" as powerful as modern games consoles like the Xbox 360 and Playstation 3, according to graphics genius John Carmack.
In an interview with Tom's Hardware, Id Software's John Carmack—one of the most knowledgeable, influential, and affable graphics programmers of the last twenty years—spoke at great length about the power of mobile hardware (and more) with Tom's Guide.
We have an embarrassment of riches when it comes to mobile development. We have more power than you can afford to take advantage of. We can afford to put all of this optimization effort into the consoles because we know that we're going to make tens of millions of dollars by doing all of this, and while there are a few iOS apps that have made money like that, you don't go into making an iOS app expecting to make tens of millions of dollars, and you also wouldn't want to spend the extra year hyper-optimizing things. But they are so powerful already that you don't need to, and that's obviously going to be getting much better still, where you've got the quad-core CPUs and the crazy graphics hardware. There's been incorrect hyperbole about the power of these devices, where people are saying that they have console-level performance. The iPad 2 has about half the performance power, and that's a ballpark estimate. But that does mean that mobile devices coming out, certainly next year, will be flat out more powerful, and they'll probably be powerful enough where you don't even need the hyper-optimizing, that you could do a fairly easy port-over of your technology and assets. The biggest issue is going to be total distribution and storage space.
Interview: id Software's John Carmack [Tom's Guide]