The Vista model approach is far superior than Apple's sudo model if you ask me. And here is why...
When Apple OS X prompts for elevation and it has accepted, the default configuration for the built-isudo actually has a period of time in which you can run ANY privileged tasks repeatedly without having to provide your credentials again. It is possible to manually go in to the OS and remove this grace-period, but the very fact it allows ANYTHING to be executed with elevated privileges shows a weakness in the ability to control the per process security context that Vista provides.
Windows re-prompts for elevated credentials for each and every process. More importantly, when Vista prompts the user for elevation of privilege, it's not actually doing it on the native desktop as you would be led to believe. (Which OSX's sudo does) It's actually a neat little trick. They take a screenshot of your working desktop, then flip to a secure desktop. Moving to the secure desktop eliminates attack vectors born from malware that may use API hooking, keystroke loggers etc. to capture credentials or force a security decision that the user doesn't want to make. Vista then paints your desktop on the background and then gives you the elevation prompt over top of that. It APPEARS as if you are on your desktop, when you are not. Nice trick.
In my opinion, that is much more safer than OS X's sudo.
