After installing M2b3, I noticed my notebook was running much hotter than before. Investigation showed that this was because dynamic clock control was no longer being used on the ATI graphics card. Rolling back to earlier versions of the fglrx package gave the following measurements with the notebook idle:

Version    Core Clock    Memory Clock    Power

8.930      100MHz        150MHz          19.8W
8.950      100MHz        150MHz          23.2W
8.951      600MHz        800MHz          34.4W

I realise there is a dilemma here - if you don't use the latest driver, you won't have support for the latest ATI cards, if you do, battery run time will be greatly reduced.

For reference, my machine has hybrid graphics:

  Intel Corporation 2nd Generation Core Processor Family
  Integrated Graphics Controller [8086:0116]

  ATI Technologies Inc Whistler [AMD Radeon HD 6600M Series]
  [1002:6741]

(using the IGP gives an idle power of 24.2W - which makes you question the utility of hybrid graphics).

I've not managed to find anywhere to report this bug upstream.