I just committed support for view filtering yesterday. You can now filter the displayed articles by all, unread, articles posted today and articles retrieved since the last refresh. See the View menu for the options or click on the new widget that appears on the article list header.
This change involves a database upgrade to add a new createddate field to the messages table but this change is fully backward compatible so it is perfectly safe to switch between 2.0 and 2.1 after this change.
(The database upgrade itself has a couple of minor issues: the table upgrade has no feedback UI and Jeff reported a problem where you end up with two Help menus afterward for that session. I'll be looking to fix those later).
Now I'm switching gears and spending a few days fixing 2.0.3 for a release next week.