I recently set up a second monitor on my machine.
Well really, I commandeered our Samsung tv. It seems to make sense to have both screens in the same place, since the couch is directly opposite both. The only small downside is that it might be distracting trying to work while your other half is playing Skyrim.
I was really surprised at how well Awesome works with two monitors.
After attaching the second monitor, I loaded into Gnome 3 (as girlfriend uses this it was the priority). I used the Nvidia config tool to set up the second monitor and save the results to the config. There was some setting up to do with Gnome as the defaults were a bit nonsensical; to reach the "sweet spot" (or whatever it's called) in the top left corner I had to trawl the mouse all the way across two monitors. It was easy to fix with a small hack. There's still some issues I have with it, such as the log out box appearing on the wrong screen.
Then I loaded Awesome. There was nothing to do. Just worked. Even stretched my wallpaper across the two monitors. I had to find some panoramic ones to cover the whole two desktops.
Awesome treats the second monitor as a second monitor. It gives you another top panel with another selection of tags on the other side, rather than trying to combine them into one.
Instead of dragging windows between monitors, you have the really cool shortcut of Win + o which shoots your current window across to the other monitor, automatically fitting it into the tiling scheme of the other. This is shockingly useful.
Can't see myself leaving Awesome anytime soon.