On "premium awards" to the US and the Caribbean, you can definitely upgrade according to your Preferred window-- 7,3, or 1 day(s) prior to departure. On saver awards, US Airways does not allow you to upgrade. However, as many others have mentioned here, on flights with good First Class availability, nice gate agents may upgrade Preferred members in an effort to keep their loyalty to US Airways, though technically, they are not supposed to. I love the US Airways agents at Fort Lauderdale, most of them are very nice and many times they have even upgraded friends of mine who had no Preferred status and were on saver awards since the agents knew that my friends and I were on the same flights. Do note that these were all A321-operated flights, I don't think they would be able to bump my friends to the front of the cabin on B757s with just 8 First Class seats.