I've been testing a new computer setup for use when I'm working at libraries. I have a 13" Macbook, an iPad, and a Mi-Fi personal 3G wireless router.
I downloaded an app for my iPad that turns the iPad into a second monitor for a Mac, but it requires a Wi-Fi connection to work. So I've set up my Mi-Fi into a local router and I've connected both my Macbook and my iPad to that wireless network, so now I have a second "screen" and 3G Internet access.
Dual screens and 3G Internet pretty much anywhere in the states...
I think it's a great portable office setup :)