What? Unity is the first shell that actually properly supports multi-monitor setups. I use it with two monitors actually and it's been just amazing to work with.

The edge resistance. The weird, inconsistent, PITA edge resistance it puts in between screens.

Whoever thought that was a good idea needs to be thrown off the team, forever. It drove me absolutely nuts until I finally managed to get rid of it.

I use FVWM2 at work with two monitors, when I have time I plan on moving to xmonad. I've used Dropbox and a few other lightweight WMs too. They all worked OK with my dual-monitor setup.

I've used Unity at home since the beginning, and it's the single worst multi-screen experience I've ever had. I only stick with it in hopes that I'll get to watch it evolve into something useable.

So, you not tested it with KDE. I was using dual monitor setup for a year with KDE and it's amazing ! The only problem that I had it's thanks to crap ATI drivers.