Ubuntu Unity will default to either a single window for a single foreground application on netbooks, or to multiple windows for a multi-foreground interface on a desktop or laptop. Users can choose whichever of these environments they wish.
Let me make this clear: Even after Canonical makes Unity its default desktop you can still switch over to an ordinary GNOME desktop.
You may not want to. The Unity interface is simple. Too simple perhaps for experienced Linux desktop power users. But, if all you want is straightforward, direct access to your applications, it works quite well.
The Unity display is also meant to use less screen real estate, while still conveying useful information to users. The effort to to make this happen is called Project Ayatana. According to Shuttleworth, there are two main aspects to this: Notifications, the sole purpose of which is to notify you of transient events, and Indicator Menus. These combine persistent awareness of a state with a set of options for modifying that state.
This is used primarily on Unity's left application bar. On this bar, you'll find icons for your desktop's default applications. There's also a full-window interface that gives you access to your programs by category.
When you have an application or a full window open, you'll still get a top menu bar that will look basically the same from one program. Indeed one of the reasons why Ubuntu went its own way from GNOME is that GNOME 3.0 won't support Ayantana's global menus.
The interface is also designed for 16:9-sized interfaces. While its still usable in the older 4:3 displays, it looks best on 16:9.
Shuttleworth also plans to support multi-touch, which was introduced to Ubuntu in the most recent version as Utouch. "I think in the near future all laptops will have sophisticated multi-touch hardware. All the hardware vendors that are working on touch are talking to Ubuntu."
So, what will it all mean for you as a user? While I like Unity, it's too simple for me. But, then again, I'm not the audience for it either. It's meant for people who want to do things on their computer -- no matter whether that computer is a tablet or a full-sized PC -- and don't care about being able to get at the nuts and bolts.
Perhaps one way of looking at it is that today the Mac desktop is like a car with power-steering, power brakes, an automatic transmission and all the rest. The Windows desktop is also a manual transmission car with a bad habit of breaking down. And, the Linux desktop circa 2010 is a manual transmission truck -- you can do anything with it, but it helps to know what you're trying to do. Unity is trying to make Linux as automatic as a Mac, but at the same time it's also trying to make it possible to run any computing device with it as the interface.
Will it work? I'll be watching closely to find out.