I'll bite... I use windows XP dual monitors at work and Gentoo Linux dual monitors at home. Both setups are nvidia video cards.
Work: I use the nvidia config utility to give me viewports. These are not as nice as the ones in XFCE4 mainly as they have been grafted in, and many windows apps don't like them, they do work. Multi-monitors are setup using windows builtin tools for that. Main screen on the left, secondary on the right. This means I need yet another third party program to mangle backgrounds so that they display correctly. (hopefully this has been fixed in win 7). I also used tweakUI from MS to setup my mouse to be X style with autoraise. This also only mostly works. Excel is my biggest grievance, I cannot have one workbook open on each monitor and retain DDE(dynamic data exchange, paste values, formats, etc) between workbooks.
Home: I have enabled dynamictwinview and used nvidias tool to set up the dual monitors. Main on the left secondary on the right. The background image just works. Full screen on a single monitor(mplayer, vlc, wine games, etc) all just work. XFCE4 provides great support for viewports. With the newer nvidia drivers, I'm not sure I even need the nvidia tools, and could just go back to using xrandr. In general everything works well on linux.