From my members, because we're not subjected to the same work conditions as airline pilots are, I don't hear many complaints, but I do know that it is a significant concern. I personally have experienced having to work for long periods of time. It takes quite some time to recover and you make more mistakes near the end of 30 days of being on duty than you do after five days' work.
On April 15th, 2010. See this statement in context.