Email has gotten to such ridiculous levels for some people that plain old spam filtering isn't enough. I like Google's idea of Priority Inbox, where it helps you decide what is important and what's not, but I'm not so sure about the way it divides the inbox into tiers. I'm sure they tried it, but I wonder how it would look if they just sorted the inbox by perceived importance, highest at the top, lowest at the bottom. There's not always a clear distinction between Important and Unimportant, but some things are more important than others. With just a continual gradation from Most Important to Least Important, no matter how much Important email you get, the most important stuff is always at or near the top.
Mokalus of Borg
PS - I don't get nearly enough email to test this.
PPS - And I'm not going to try getting enough.