The ONLY problem with the .us is that people are more used to .com, and might type the address wrong and get the competition. On the other hand, a .us address is unique enough that people remember it. It's a great TLD for people doing business only in the US.
The domain US.COM was bought by CentralNic a number of years ago, along with similar domains such as UK.COM, FR.COM and EU.COM.
In terms of competing with genuine domain extensions, these subdomains are never really going to match the success of 'real' domains but do potentially offer you the chance to get hold of the domain you really, really want, when all the main domain extensions are already taken.
R.