My wife and I had booked roundtrip first class tickets using FF miles on US Airways from Dulles to Charlotte and then nonstop to Honolulu. We were notified the morning of the return flight that the flight was cancelled due to "mechanical" problems.

Our options for return flights were to leave late that evening and go first class from Honolulu to Phoenix, then coach from Phoenix to Dulles or to wait two days and have first class seats on both legs of the flights. We were told that there was nothing else available. (Hard to believe that there was NOTHING else available, but that is what customer service insisted)
We close to leave that evening, but this put us back home 6 hours later than the original flight and caused quite a bit of inconvenience, not to mention flying coach from Phoenix to Dulles.

I am entitled to any compensation for the inconvenience that this caused, and if so, what should I be entitled to?

This is a US airways-specific questions. You'll get more feedback in the US airways forum. American carriers usually don't compensate for delays. Some US airlines might throw a small voucher or some miles but not always. As for downgrading, again you should check in the US airways forum what is standard. In your case, since you flew First on the HNL-PHX, there is probably no difference in miles flying F to PHX, or all the way to IAD, and US airways will be reluctant to give you any compensation.

OP created new thread in the USAir forum:

http://www.flyertalk.com/forum/us-ai...pensation.html