Night and day. Vim on one screen and a multitude of things on the other: Matlab, a Windows VM, Web Browser, Terminal, etc. Combine dual screens with a tiling window manager (XMonad, Awesome) and you're laughing.

As far as physically managing two screens: I have a laptop dock at my desk which has a display port. Drop my laptop in and instant additional screen. Come home and sit on my couch, plug in HDMI and use my TV as a monitor, really great for web development.