One of the most obsessed over features of Windows is its boot time, according to Windows chief Steven Sinofsky. As such, he says in a blog post, Windows 8 will boot so fast it will make the relatively spry Windows 7 seem Vista sluggish.
According to Sinofsky's post in the Building Windows 8 blog, the way Windows 8 achieves such super-fast booting is that it doesn't quite shut down in the traditional sense. Instead, it uses a fast boot that's a hybrid of "cold" booting and hibernating. Green minds should rest assured that there's "effectively zero watt power draw when off," while those who like the clean start of a real boot up can look forward to a "fresh session after boot."
Here's the Windows Team's visual comparison between a cold boot and a new hybrid fast start: