Too many things wrong with this concept
For starters, it encourages users to leave computers running 24/7. That's going to piss off the environmentalists - and I'm definitely on their side with this one: what, 8 hours of use in an office and then another 16 burning power just so it can run an update? No thanks.
Secondly, if your OS didn't take so damn long to boot up more people would turn it off at the end of the day. Last time I checked, it was considered good practice to reboot Windows boxes regularly so we shouldn't really leave them running constantly. How's that play into the 'we'll do it when the machine isn't being used' policy?
Thirdly, as already pointed out, a machine that's powered down is nicely secure. Leave it running and there's a larger corporate attack surface to have to keep tabs on.
Lastly, why the heck can't MS do updates like most modern OS's and apps? You know, quietly and in the background while the machine is in use? I know mine does - but only because I look in the logs. I'd not notice it happening otherwise.
Oh - and all this is before we even consider the (very real) risk of MS buggering the update and simultaneously leaving all users high and dry on a busy Tuesday morning. I'd hate to be tech support when those calls start stacking up.
Biting the hand that feeds IT
