Definetly profitable (for some anyway) you just need patience and commitment to going after end users as forum sales will get you by, but very rarely make any good sales on the forums, sold 1 i got for $50 for $1200 to another domainer recently.
Business do use them, you will se a lot of foriegn companies using them also.
Dont get me wrong, theres not many big companies use it, but lots of the big companies have there .us domain, so some importnace there.
.us is definetly a long term investment, or a short term if youre really good at getting end user sales, i dont really go after end users very often, as i'm in it for the long term, years, not months so todays sales dont play any part in what i value my names at.
and .us is growind daily, by numbers of names registered, and by pages being created on the cctld. Theres 1 big change we need and it involves someone else getting the contract to run the .us cctld ext.
Last but not least .us is the OFFICIAL country code for AMERICA, lost of other domainers say .com is, but well, they are all wrong.
When i go after an end user i always play on the .us being the oficial contry code for america, as it does make those patriotic companies have a little think about it
Good luck if you decide to invest in .us, no time like the present