The way I see it, i would like to set the 3D view (maybe two 3D views on the first monitor), and floorplans on my second monitor. This for an overall look of my project to view the effects of changes I made to the project floor plans. But this can work with anyway you want to overview your project. Like elevations on monitor 1 and sections on monitor 2 or whatever you are using.
Swapping the properties box to the second monitor while working on the first monitor is not working well, because you have to swap your mouse to the second screen constantly to adjust something. It's more the way to have a quick look like i mentioned above.
I already uploaded this as an Idea a few days ago @ http://forums.autodesk.com/t5/revit-ideas/dual-monitor-support-for-revit/idi-p/6326115
I just wanted to address this over here as well.