To me, the single biggest fault -- one that very nearly made me just get up and go the the nearest Apple store, right then and there -- is the fact that Windows STILL will force a reboot of your machine while unattended (I did figure out how to turn that off, but your average user would not be able to do it). Whoever decided to make it default to forcing a reboot is unforgivably stupid.

Not to mention: why is it, that in 2010, we have an OS that still requires reboots at least 3 times a week?