Lion users, have you ever tried to drag a file between full-screen apps? It's a bear to do, especially with a trackpad. Matthias Gansrigler at Eternal Storms (no stranger to TUAW) has solved this problem with an app called Yoink.
Yoink simply watches for you to start dragging a file and when the app notices this dragging motion, it opens a small drawer on the side of your screen. You can drag files to the drawer, and even stack multiple files in there, then switch spaces and drag them back out. It's simple, it's effective and it solves the problem quite elegantly.
Apple OS X Yosemite