The lack on Windows of quick keyboard shortcut access to multiple open buffers and virtual desktops make multiple monitors seem important. Navigating by alt-tab and with the mouse is just too slow. In the X11 world the other buffer/virtual desktop/screen of stuff you want to see is one or two key presses away.
I have never felt a big benefit from multiple monitors, or even especially big monitors. 95% of the time I'm working with text, and I can only comprehend one window of text at a time. As long as I can flit around between multiple buffers, tabs, or desktops without my hands leaving the keyboard I'm fine.
I've run Linux forever and always enjoyed two monitors. I use WindowMaker and have have 7 workspaces (Main, Browsing, Communication, Development, Email, Shells, Misc.). Keyboard shortcuts for everything as I despise the mouse.
Most of the time I'm in "Development" and the left monitor is a fullscreen terminal with documentation/revision control/program output and the right is fullscreen gvim.
Nothing is more important to me than resolution though. I can't deal with anything less than 1600x1200 and almost always run 1920x1200 on everything (including laptop).
I have never felt a big benefit from multiple monitors, or even especially big monitors. 95% of the time I'm working with text, and I can only comprehend one window of text at a time. As long as I can flit around between multiple buffers, tabs, or desktops without my hands leaving the keyboard I'm fine.