Traditionally, all the action in GUIs takes place in two major layers: the Desktop plane and the application plane. The application plane contains the windows that we spend the bulk of our time interacting with. These windows overlap and jockey for space and focus, constantly competing for our attention. In OS X, you can use Exposé to see all the contents of the application pane at once. In Windows 3.1, there was an option to tile all open windows so that you could get a similar view, although people didn’t use it often (because it was awful).

Both Windows and OS X provide quick commands that let you hide the entire application plane in one fell swoop, exposing the Desktop that lies beneath it. Compared to the application plane, the Desktop is a relatively simple place, unless you’re one of those people who lets icons pile up by the dozen. In addition to being a repository for shortcuts and fancy wallpapers, the Desktop acts as a backstop; you feel confident that there’s no other plane below it, that it isn’t hiding anything from you. (I think this is partly why Active Desktop never caught on; people didn’t want to loose the rooted feeling that the desktop plane provides.)

In OS X 10.4, Apple introduced Dashboard, a plane that appears above the application and Desktop planes. Dashboard contains a bunch of Widgets, which are basically gussied-up Desk Accessories that no longer have to fight for space within the application plane. This is nice because you don’t want to have to rearrange a whole bunch of windows just to play with a sliding puzzle or check the weather — now, they’re just a keystroke away.

More and more applications can be found living in the transient plane. Somewhere in between the application and Dashboard planes, there’s a place for little windows that pop up, give you some information, and disappear again. LaunchBar, Growl, Twitteriffic, and Google Notifier all live in this space, as do the OS X Dock and Windows Taskbar (when set to auto-hide). Transient applications are useful for pushing information to you and letting you respond to it with a quick click or keystroke, but they can interact with the application and desktop planes in a way that Dashboard widgets can’t. Unlike the dreaded “always on top” option, though, most transient applications these days actually behave in a transient manner and don’t eat up permanent space on your screen, which helps to avoid conflicts with the all-important Application Plane.

All of this is a roundabout way of getting to a very minor complaint I have with Pownce’s desktop app: It should totally live in the transient plane, not the application plane. I’m still not sure if Pownce is supposed to be a Twittery microblogging site, a high-concept message board, or an IM client, but whatever it is, it’s meant for quick hits and rapid responses, which says “transient” to me. Living in the application plane means that it doesn’t draw my attention when something important (a new message) happens, and it just distracts me the rest of the time. It also looks different than all my other “normal” apps, which just makes it seem that much more out of place. If it popped up and then hid itself like Twitteriffic, I could stop worrying about whether I’m missing messages, and get back to trying to figure out what the point of Pownce is in the first place.