Currently, left-clicking the main link at the top of an article entry will mark that article as read. This opens the article in a new tab, but also focuses the new tab, forcing me to switch tabs back to The Old Reader if I want to open more than one thing before I actually read them (which I pretty much always do). A middle-click in all major browsers opens the link in a new tab, but keeps the current tab selected. If this also marked the article as read, it would be the most efficient option by a wide margin!