How much is a bigger screen worth?

I'm planning on switching to a MBA, but there's something limiting my progress.

The amount of money I have is dictated by the amount of money I get by trading in my PC, which means that I might not be able to have as much money as I want. I can get a 11' MBA for the same price as the PC, but for $100 more I can get the 13' model. Is the extra screen estate worth the $100? I'd appreciate it if you could share your experiences. Thanks!