Miles are valid for 18 months; any activity in the account resets the 18-month counter, so you could take a flight on US or any partner and credit to US, buy something in the shopping mall, do a redemption, etc once every year and a half to keep the miles alive.
Partner award chart is here
http://www.usairways.com/pv_obj_cach...wardtravel.pdf
Note that it lists Qatar as a partner but there is a footnote that award travel on Qatar is "temporarily unavailable." It has been in that status for a long time if memory serves me, so it is anyone's guess as to if/when it will be available again.