I picked up this story from Neowin. It claims Vista SP1 adds a whole 6 minutes of battery life to a laptop. Meanwhile this is what it does to one of my desktops (from the error log):
Event ID: 6
Source: Kernel-Processor-Power
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Some processor performance power management features have been disabled due to a known firmware problem. Check with the computer manufacturer for updated firmware.
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I’ve noticed no changes in the way the computer operates (all power options are off anyway).