Ray:

Anyone who is doing a critical business process online that involves substantial dialog between individuals should NOT be using email at this point in history, and many no longer are.

If you have work to do with others, online, try workspaces. There are many different types - from Groove if you like client-based mobility, to SharePoint if you like using Websites... you'll only visit eMail as a low-priority background task, much as you do when sorting through your physical mail at home. You'd never do important work through your home mailbox, would you?

Update 10-02: Sean and Scott add:

I've tried probably 300 different ways of organizing my inbox over the years and nothing works all the time for every situation.... What I want is one tool that does what Groove, Sharepoint, and Outlook do for me that works in Offline and Online modes and is one tool. It's really more of an issue of focusing on what the work is that people use the tools for as opposed to the tool itself...