I had a good experience on the AA/US FF alliance in March. My wife needed to travel RDU-ORD-BWI on an open jaw award, in time to go from home in Raleigh to see my older son in a concert in Chicago and then to be in Baltimore to pick up my younger son at the hospital. No one had the schedule to do it, until I asked the US CSR at Dividend Preferred Service Center if she could go RDU-ORD on AA, then ORD-DCA on AA then a connection DCA-BWI on USExpress. She said the rules allowed interline connections, and it worked out great! (US had no flights ORD-BWI Sunday morning, and AA does not fly that routing)