Before Windows 7, I didn't bother moving windows around too often. I've always had Trillian on my secondary monitor though. With Snap in Windows 7, I move stuff around a LOT, especially browser windows for watching movies. I almost always watch video on the right monitor as it's much larger and full HD.
In general, my left monitor is my "general use" monitor. Trillian is always docked on the left of it, the taskbar is set to it, Firefox is always on it (I tear tabs off into their own windows when I watch videos), mIRC is always on it, Grooveshark is always on it.
The right monitor is for work or gaming stuff. Word, TF2, Netbeans, all of those stay on the right monitor to make full use of the larger resolution. I especially like Word over there, because with Snap I can have two Word windows side by side perfectly, and still see a whole page without scrolling horizontally.