...including the feature that I find the most interesting: if you try to execute an action that requires administrator privileges you will get a login dialog and be able to temporarily become administrator just for that action (see picture below, click for full size).

Yes, I know that Linux had this basically since forever but it's really good news for everyone working with Windows. This does not yet work properly everywhere (mostly you get disabled controls on places where you should not mess things up) but it's a great sign of the things to come.