The so-called "desktop metaphor" of today's workstation is instead an "airplane-seat" metaphor. Anyone who has shuffled a lap full of papers while seated between two portly passengers will recognize the difference--one can see only a very few things at once. The true desktop provides overview of, and random access to, a score of pages. Moreover, when fits of creativity run strong, more than one programmer or writer has been known to abandon the desktop for the more spacious floor.[1]
This is so very true that it nearly boggles the mind. This is behind the push for larger screens. This is behind the proliferation of icons in the system tray. This is behind the desire for multi-headed displays (both those used as a contiguous desktop and those used disjointly). This is even behind my own use of virtual desktops. We simply cannot see enough on the desktop.
Not only can we not see enough, we cannot find things easily enough. That is why I, and those like me, sort windows onto virtual desktops. Those who use multi-headed displays disjointly fit into this category. We cannot find things on one desktop, so instead we split the work into n desktops, in hopes that on any given desktop we can see everything related to a task or subset of tasks. This is why people hate having overlaping windows, and thus want bigger screens, if the windows do not overlap, they do not have to "shuffle pages."
The desire to not "shuffle pages" is in turn why the system tray gets used. We cannot fit everything we want to run on the desktop without overlap, so we "minimize" some of it. The area to minimize things into is limited, so we further collapse some of them into the system tray space. Never mind that this is an abuse of the system tray, it saves space, and space is at a premium.
It is amazing how much of modern UI design, of the requests I see developing Gaim, are explained by this one relatively simple analogy. We do not have desktops, we have airplane seats. And that means that space is always going to be at a premium.