Vista DRMWindows Vista puts a lot of work into preventing what it considers to be "unauthorized" access to copyrighted material. In an attempt to plug every leak (an impossible task) the DRM system pervades every aspect of the OS, from the kernel upwards.
One disturbing aspect is the constant scanning of the system to determine if there are any fluctuations in voltage, unexpected register content, etc. Over time this totals to significant energy consumption. Also consider that the CPU requirements are significantly higher than would otherwise be expected, meaning that power consumption gets even higher.
We often don't pay attention to how much power extra CPU cycles burn in a PC, but it becomes painfully obvious when traveling with a notebook computer. I once had a PC which made it clear whenever I scrolled text in a web browser, as the fan in the power supply would go up in pitch with the extra load from the CPU. So the power difference of CPU use can be significant, despite it being hidden in amongst the hair dryer and air conditioning in your electricity bill.
If 90% of the new computers in the world (Microsoft's approximate market share) are going to be running Vista, then what will be the extra power consumption? This is a worldwide expansion in energy consumption for the sake of the MPAA.