When you launch an app on the iPhone or iPad, there is a transformative effect of the device becoming what the app is. Fraser Speirs sums it up best:

The thing is that, when you use an app on an iPad, the iPad becomes that thing. Maps makes the iPad a map. iBooks turns it into a book. Brushes turns it into a sketch pad.

The general gist of Apple’s “Back to the Mac” event was that the great ideas of iOS are coming back to the Mac. One of the major ideas discussed was full-screen apps.

In my opinion, the best way for an app on Mac OS X to scale to full screen is if it is designed to be a one-window app in the first place. In turn, Bjango states it best in their argument for a one-window iChat:

I’m finding more and more that the best way to design desktop apps is to imagine you’re building them for iOS.

I imagine Apple will refine their multi-window apps into one-window and encourage developers to do likewise. The iLife suite has long focused on using one window, and the new iPhoto ‘11 demonstrates a graceful move to a full-screen app.

Another example of consolidating apps with cluttered UI is the developer preview of Xcode 4. If you’ve ever used Xcode, you know that things can get carried away with multiple windows and palettes. Xcode 4 aims to reign that in with a single window interface. Imagine this (pay attention, developers): I bet Xcode 4 will ship its final version with Mac OS X Lion, and that one of the surprise kicks will be a full-screen coding environment.

Maybe this reduction to one-window apps is why we haven’t seen an update to the iWork suite alongside the new iLife. Perhaps this is also holding up development of a new Final Cut Studio?

The fact of the matter is that Mac apps should start preparing for one-window and full-screen interfaces, especially since Lion is going to train users that the green zoom button is meant for full-screen.