When successfully logging in or unlocking the screen, the actual desktop is not transitioned, but an abrupt change is performed. My initial transition mockup uses zoom for the actual desktop, which is appropriate, but the "system level" authorization dialog actually slides up on a level above it, which in restrospect doesn't make sense.

http://jimmac.fedorapeople.org/gnome3/login.webm

I'll provide a mockup of a transition that I think makes more sense -- fade the authorization dialog out, keeping the system grey texture and zooming the desktop in from the center.