To me, it's the ability to put my current "focus window" exactly center what makes the curved screens so attractive, with the 32-38" size range always feeling just about right to me. My neck starts aching if I have two screens, making me end up using one as the focus screen and the other as support. While three 27"s in a row seem slightly excessive "screen wall" to me, but some like that...
I guess it really depends on your workflow. My own preference is to use my left monitor for source code and shell windows and my right monitor for browser testing. That does mean I tend to spend a significant amount of time looking to my left.
