Having multiple monitors isn't good eronomically IMO. I always prefer what I'm working on to be on direct center, and I don't really see the point of having other stuff that isn't direct center. I prefer to alt-tab.
It's great for keeping API docs open while I'm working without leaving my editor.
Having the center monitor on an arm just lets me adjust it's height when I move between leaning forward, slouching, or sitting straight, standing, etc.
A single monitor is limiting as it requires more context switches as I swap out windows in my viewing area. It's much nicer to just leave all the important windows open in a nice grid that spans multiple displays.
I just have found that if you want to read something, I prefer it to be on the center monitor anyways, so what's the point in having multiple monitors?
Plus, I prefer to work on my laptop screen, because it's more flexible - I can put my feet up, move around, change positions easier.
Just my own personal preference
The only time I use the side monitors for anything else is if I'm following along with a screencast.