The A6 chip which debuted on the iPhone 5 earlier this month can do some pretty clever tricks, stemming from a heavily customized ARMv7 design. Benchmark data suggests that the A6 can dynamically overclock itself to up to 1.3GHz and downclock to just 500MHz, depending on workload.
This is nothing new in chip design, of course (just ask Nvidia or Qualcomm). But given that Apple designs its chips in-house based on ARM and Imagination Technologies blueprints, it shows just how far along Cupertino is versus companies that use off-the-shelf chips which are not as power or performance-efficient as the A6...