I've often wondered why the page has to refresh to log you back in. It seems logical that the system already knows who you are, and a refresh isn't doing anything more than requesting fresh content from the server.
I haven't dug into this enough to know whether or not the banner is being "pushed" from the server or if there just happens to be a timeout delay before it appears, but could the development team use Comet or server push or Websockets to "push" the updates to the client instead of requiring a full page refresh?
The answer is that they're already moving in that direction, but they're targeting features that have the most impact on usability.
In fact, I've seen a lot of improvements in this area. For instance, one used to have to refresh to see the question and answer scores and to see if new comments were made. While a "new answer" banner would appear to alert you that a new answer is posted, actually viewing that answer required a full page refresh.
Today, question and answer scores are pushed to the browser, using what I can only assume is Comet (or some form of long poll, or Websockets).
# This fired automatically while I was typing, and it appears to save my draft,
# judging by the response
Additionally, new comments and new answers are instantly available through an AJAX call invoked by a mouseclick. Reputation, flag counts, suggested edits all appear to change dynamically.
Therefore, judging by this steady progression towards an "app feel" and away from a "website feel", it stands to reason that it's just a matter of time before the development team gets around to making this log-back-in process more smooth and seamless.
UPDATE: From the official development team, they're using Web Sockets.