To test power consumption today we are using a Keithley Integra unit and we measure power consumption from the VGA card inputs, not the system wide drain. We measure results while gaming in Crysis Warhead and record the results.
The card doesn't demand much power, that is for sure, idling with a drain of 8 watts. Under load it rises to 24 watts. Watching a Bluray disc with acceleration enabled causes a drain of 14 watts.