World of Warcraft has a "windowed but full screen" mode. It *looks* like full screen mode (in that it takes up the entire screen with frame or anything), but it functions like windowed mode in that you don't have to alt+tab to use other programs or things on the other monitor. It also has a normal windowed mode where you can move it around on the screen and such. There's a minor framerate hit for doing that, but most of the time it doesn't matter.

Something like that would be nice in Elemental too. Presumably we'll be able to see what type of controls they have in mind once beta hits.