Gmail pitches Priority Inbox as a way to skim the cream off of your e-mail and let you get to the important stuff faster — like a reverse spam filter.
I have not seen any publicity surrounding one very useful feature of priority inbox — the ability to filter mail into distinct categories right on the main inbox screen. By default, Gmail shows you important-and-unread items first, then starred items, then everything else.
But you can customize the first two sections by clicking on the disclosure triangle next to the section’s name. I like to have all important items (whether read or not) first, then all unread items, then everything else. I don’t use stars much, and I never use stars on unread e-mail, so I did not see the point of having starred items called out. As I read my unread-and-unimportant items, they move from the middle section to the bottom section, but my important items remain in one place.
These filters only work with items in your inbox; once you archive an item, it only shows up in a search of “all mail.”