One-time “View read” button
Google Reader had a nifty feature: “View read” button that didn’t switch feed view mode to “Show read” permanently.
Case in point: I want to find some recent article marked as read (intentionally or not).
Current behaviour: I need to go into menu and find “Show all” item, find the feed entry I need then switch back to “Show unread” mode.
Desired behaviour: I press button “View read”, look through read articles, then, after reloading feed or switching to another view only unread articles are shown again.
I personally don’t see any use in permanent “Show all” mode, but that’s just me =)