The problems lies in right management. Vista is pretty stable - only if you use it in lock down mode as a user with limited rights. As long as you use it with an admin account though, things can go wrong very soon.

As single user on a machine, people tend to use an admin account though, since it makes installing stuff etc. not as long-winded. UAC is a good idea, except that it comes way too often and makes people get annoyed so they don't even thing when they click on OK. Similarly, on OS X, we have password prompts, which don't occur as often, but also guarantees authorization. You can also authorize yourself as an admin even when the current session is from a limited user.

which is also the exact thing that i do. both my desktop (winxp) and my macbook are put into standby/sleep when im done using. both take two seconds to wake up and even the desktop draws less than one watt.