As a former federal inmate (Read my story via The Market is Not Random), I was able to witness the expanding overcrowding of the system. The United States Sentencing Commission has been stating for many years that prison sentences are too long, and that non-violent criminals (like me) are prime candidates for alternative sentencing. In fact, regardless of crime, the majority of Americans believe a prison sentence of 2.6 years is long enough.
That said, I don't see that as the complete problem. Once released, federal inmates are subject to supervised release sometimes in excess of 10-15 years. The ability to track the ever expanding populous of inmates does a disservice to tracking the non-reformed. If one was to believe that prison did not lead to reform, then the proper conclusion is that all prisons (including myself) should be executed, regardless of crime.