"On Tuesday, Google is launching a remarkable new feature in Gmail—a system that sifts through your daily flood of incoming mail and picks out messages you're likely to deem important. The new system, called Priority Inbox, is the opposite of a spam filter. Instead of looking for keywords that mark unwanted mail—'Buy now Vic0din 3o% of!'—Priority Inbox looks for signals that a message is especially valuable. Among other things, it analyzes your experience with a particular sender—is a message from someone whose mail you tend to open and reply to?"