I agree.
Boot up time should be mostly irrelevent in a modern OS. I reboot maybe once a week at most. Sometimes go months without rebooting. What matters more is the ability to do hibernate or sleep...
It's much much more efficient and with hibernate it's not any more power-hungry then shutting down. Think about start up time for all your applications. For instance when I play Doom3 it starts up much quicker and maps load quicker after I've run it once and quit then when I run it right after a reboot. This, of course, is due to memory management and since I have a gig of RAM large portions of 'used' memory are just cache in case I want to rerun stuff I stopped running earlier. When you reboot you loose all this and you have to end up re-reading it all back into ram to get everything as fast as it should be again. When you hibernate/sleep then you don't have to worry about it.
What Microsoft should do to make things much easier for Vista users is remove the requirement that you have to reboot during most updates and driver installs if at all possible. (I understand that sometimes it's unavoidable)
I mean that I can install Debian from a netinstall cdrom faster then I can install Windows XP on the same computer even though with the debian I am pulling all the installation files from a ftp server on the internet. With Debian I'd have to reboot 2, maybe 3, times to finish a install... 1. boot up the cdrom, install os. 2. boot up OS, update OS with most recent kernel and other things, 3. reboot up OS and it's finished (and that's only if I decide to update the kernel to a different thing then default). With Windows XP on the other hand I would have to reboot more then a dozen time and I'd still have to pull down virus scanners and such and probably those would require a reboot themselves for whatever reasons.
Plus if MS is able to do that then it would be much much easier to convince people to keep their machines up to date. If there is a critical update or whatnot then you could do something like have a icon pop up on the task bar. So that when somebody is working on a word document or a report or something they would just hit the updates(2) button, it would warn them to save what they are working on 'just in case', or whatever and continue on with their work as the system patches itself. No reboot, no fuss, no muss. Like nothing happenned.