Deep inside the Windows 7 Public Beta: an in-depth tour
 

At the right end of the taskbar is what has become known as the system tray. The tray's proper name—the notification area—gives a hint of what it was intended for; it was a place for applications and the system to show the user alerts whenever it needed the user's attention. Of course, few applications actually use it this way, and even Microsoft uses it simply to provide quick access to things like the volume control and Task Manager.

This abuse of the notification area has become increasingly acute over Windows' life; applications add to it willy-nilly, rendering it a confusing mess of indistinct icons. Since XP, Microsoft has tried to reign in this icon overload, with the ability to hide icons so that they're only shown when explicitly asked for. Windows 7 takes this idea a little further; instead of merely expanding the notification area, as in XP and Vista, Windows 7 places icons into a distinct overflow area.

http://arstechnica.com/articles/paed...ows-7-beta.ars