Interesting study noted over at CNet that Windows 7 doesn't boot faster. Note this isn't the time for the desktop to appear, but for the OS to become usable. I do remember something about MS moving some of the service startup to be after the user logs in instead of before, to make the desktop appear to boot faster. Similar to Mac changing the time for the dock bounces (or was it just not showing as many) to make apps "feel" faster.
Question is, even if it's not literally faster, will the user experience of your new Windows 7 desktop appearing faster make users happy enough that it doesn't matter that it's just as slow as before?