WARNING! Google Fanboy Alert!
Google are in the process of rolling out another feature to Gmail, and I quite like the sound of this one.
You know how e-mail is divided into "real" mail and spam? Gmail is about to add another level to the strata. Priority Inbox is in the process of rolling out to Gmail users, followed closely by Google Apps users. Priority Inbox will separate out the stuff that Google's algorythms think is important, compared to everyday ho-hum emails that need to be read, just not NOW.
As with any search and classification based business on the net, Google are being pretty tight lipped on exactly how those algorythms will work, but the general consensus is that anything not sent directly to you (so cc:'ed mail, mailing lists, etc.) will be skipped over by the Priority Mail filter, while people who you send mail to and reply to on a regular basis will get picked up by the Priority Mail. Users will also be able to flag email as important or not, improving the automatic classification system.
If you see "New! Priority Inbox" in the top right-hand corner of your Gmail window, give it a go, and let us know your thoughts at the Chaotic Geek Forum.