FYI there's another company called Unotelly.com that seems to do something similar. Cannot speak to the reliability, etc of their service vs. Unblock-us.

My impression of how this works, both companies, is that when you request certain URLs they step in the middle and make a US connection to your requested URL. I was playing with a new Blackberry Playbook and while the website thinks I'm in the US showing me US prices, the App World app knows I'm in Switzerland and shows me CHF prices and also blocks me from purchasing certain apps. I'm guessing that's a port issue. They probably handle these "port issues" for only certain things like Netflix, etc.