One of the features of the upcoming Mac OS X Lion I am looking forward to is full-screen apps. There are some apps that offer this mode on Snow Leopard now, but they rest on top of all your other apps. This is one of the reasons I don't care for Windows, and rarely use any OS X apps with full-screen mode currently. I'm just not a big fan of the idea of full-screen apps being "stacked."
But Apple rethought the idea for Lion, by merging Leopard's & Snow Leopard's Spaces feature with full-screen apps. The shift in perception of full-screen apps residing side-by-side rather than stacked works for me. Even more so with the ability to move between with trackpad gestures, which I have a bit of an addiction to. [Check out the video.]
I am very glad to see the current iteration of Spaces move from a grid layout to a side-by-side layout. And filling a space with a full-screen app jives with my workflow now. I have always used Spaces as a way to segregate apps that I want to take up the fullscreen from apps with intentionally smaller UIs. For example, iCal and iTunes get their own space, whereas Twitterrific, Reeder, etc reside in my primary space.
I figure I'll have iCal, iTunes (presuming an update to support full-screen), the redesigned Mail, and maybe even Safari in full-screen mode nearly all the time, leaving the "Desktop" space for smaller apps.
It's odd that a reorganization of how full-screen apps behave does the trick for me, but I look forward to the focus I hope the feature brings.