Diners Club USA can absorbe you UA Mileage Plus @ 2 miles for 2 Club points. 2 Club points can then be converted into 1 mile in other FF programs. In the past two years, DC has been running a promotion with British Airways (BA), a major Oneworld carrier, during the Summer time where you can get 1 BA mile for 1 DC point. That means you may convert UA miles into BA miles on a one to one basis. This is the best way of interchanging miles out there in the known FT Universe.