The STM32F2 in the Imp is a Cortex M3. I absolutely love these micros, I've used them in dozens of applications over the last couple of years. Of course in this case we're kept out of the firmware (at least directly) but from what I hear the script engine runs very quickly (and so it should).

The power consumption also looks very good. My first project will be adding an Imp to my RFID cat flap which runs on 4 AA cells. If Hugo's figures are accurate, and assuming I can get a wakeup signal from the RFID module, it should run for months/years on a set of batteries.

Rob