Steve Jobs dropped a few hints regarding the speed of the A5 processor that equip the iPad 2 tablet, hints that were summarised in one slide (ed : Apple has now confirmed that the speed of the A5 is 1GHz on the iPad's technical specs page).
The A5 system on chip contains two cores that provide twice the processing power (up to 2X faster CPU) and up to 9x faster graphics while keeping the same power envelope as the A4.
This cannot mean that Apple is reusing its customised Cortex A8 core again (otherwise the power consumption would have doubled unless they moved to a much smaller manufacturing geometry).
Apple must therefore have moved to the Cortex A9 architecture instead, one which is widely known to be twice as fast as the Cortex A8 at equivalent speed (ed : blanket apology here, ARM says that the A9 is 25 per cent faster on DMIPS/MHz).
We know that the A4 in the previous iPad ran at 1GHz (Apple hasn't announced the speed at which the A5 processor in the iPad 2 is running).
A dual core Cortex-A9 based SoC would therefore be four times faster than the single core A4, assuming a perfect scaling.
Since this is not the case (remember 2X faster CPU), this must mean that the iPad 2 is clocked at a mere 500MHz or even slightly less if Apple's engineers have managed to work tweak the Cortex A9 architecture even more.
A dual core, lower clocked A5 has a number of advantages; Apple's engineers must have come up with a way to turn off one core or dynamically change the cores speed on demand.
Jobs mentions in the presentation that the A5 has the same low power as the A4 (which we shall assume means power dissipation) but we suspect that they have also reduced the power consumption.
Remember, the iPad 2 is 33 per cent thinner than the last one, which means that they will have to remove the fact from somewhere else and since they have not changed the screen and have in fact added a few more features like the cameras & the gyroscope, the battery may have been shrunk (or they are using a better battery technology).