Only after publishing a new PAGE will the permalink display and become editable.
First reported as a RC bug in ticket #6416, the issue was quickly dismissed as invalid because it could not be duplicated.
I confirm that this is a problem in 2.5 final. I have seen this on different pc's, using different browsers (IE7, FF, and Safari), in different installs of WP2.5 (including one absolutely clean and new installation), on different hosts (including one WAMP server).
The problem exists only with a new PAGE. The new POST function works as designed.
Skeptics should see the attached screen capture.