I guess it probably depends what you are planning on doing with the extra monitor.
I've been happy with one monitor and alt-tab (CMD-tab on OS X) for a long time, but recently I've realized that the extra monitor comes in really handy for certain things. For me, that's having chrome open in one window and the chrome inspector in the other (this allows me to concurrently see + play with the DOM/css/js without it crowding the display).
When I have two monitors and I'm doing this sort of work, I never say to myself: "Oh man, I'm being so productive". But when I'm without the second one, I certainly miss it and feel less productive.
I've been happy with one monitor and alt-tab (CMD-tab on OS X) for a long time, but recently I've realized that the extra monitor comes in really handy for certain things. For me, that's having chrome open in one window and the chrome inspector in the other (this allows me to concurrently see + play with the DOM/css/js without it crowding the display).
When I have two monitors and I'm doing this sort of work, I never say to myself: "Oh man, I'm being so productive". But when I'm without the second one, I certainly miss it and feel less productive.