Feels more like a bodge than a true solution.
This falls down to the whole ancient argument of a Disk Based OS vs ROM based OS. To be as easily maintainable and updateable, the MS OS is loaded and launched from disk. As a direct result, the OS fires up, loads drivers, loads services, launches the (heavy) Vista GUI, allows users to log in, then performs a ton of log-in activities involved in setting up the environment and pre-caching things.
I say this whole method can go out of the Window(s) in favour of a whole new paradigm. I couldn't tell you what that is, but as a start, you could perform the equivalent of a base heavily configured image, like how a hibernated PC comes out of hibernation, why not simply allow Windows to configure itself a fully configured memory 'image' after Windows has installed, then every following reboot, load it straight into memory? Doing so would, at the least, save Windows from needing to continually address and load tens of thousands of individual files from disk upon reboot, whilst referring to the registry and other files for the current configuration info. I have no doubt this would improve reboot speeds. Furthermore a similar scheme could take place for Application initialisation to speed that up.
Maintenance of Windows itself would suffer as a result of this, as this 'base reboot image' would need updating every so often as Windows Updates occur, or as users install apps, or as Windows indexes your disks. But efficiencies in imaging techniques could alleviate this.
I have no doubt Windows performs perceivably slowly specifically because the OS has grown out of this whole 10,000 x 30Kb file mindset that Windows is made up of - take a quick ganders in your Windows directory (System32 is a killer, my sys has over 2300 files in system32 alone).
If this idea is worth anything, I offer it for free just because one day I'd like a Windows system to fire up Office Outlook within the time it takes to sneeze. Somebody do it for me!?