Suppose you have organized some of your mail using labels that represent various projects. (Rick recently explained how to label your mail with Gmail's new buttons). You can now direct all your labeled mail into different inboxes, each of which is visible on the same screen simultaneously.
To get started, you need to turn on multiple inboxes. At the top of the Gmail window, click Settings and then switch to the Labs tab. Scroll down to Multiple Inboxes and enable it. Now you'll have a Multiple inboxes tab in Setting. You can create as many as four inboxes with filter criteria like is: star, is: draft, and is: BNET (assuming, for example, that BNET is the name of a label you had previously created).
This is actually a pretty cool feature that makes Gmail far easier to use. I wish that the inbox configuration was on the main mail screen rather than cubbied away in Settings, but that's a quibble. Not only does this help you keep your inbox clean and orderly, but it keeps your labeled mail right at your fingertips as well.