After the folks at Kensington have released the new Mac and PC compatible Dual Monitor Adapter you can use the usb port to connect a second monitor. I have a 2 monitor setup when ever I am in my office and love it. It makes it very easy to keep some things open and not take up space where I am working.
This product will also help out laptop owners who want to have a dual monitor setup and make the one on the laptop not in the pair.
The Dual Monitor Adapter is a bit high in my opinion at 119.00 but I feel sure it will come down as I gains popularity.