Out of interest name.com had a Happy Hour yesterday offering .us standard domains at just $0.99
As I don't qualify to buy a .us domain I didn't bother looking further, but I do know that namecheap are offering normal .us domains at a similar price.
I don't think there seems to be a huge demand for this extension, though I would imagine if the domain name itself was connected to the United States such as, say, nycity.us it would get some interest (though this example would probably be a Premium domain).