I think the problem with the bike generator is about the same as the gas turbine on your natural gas line. Too much machinery for miniscule amounts of power. It might make some sense simply as a symbolic punishment for Enron executives but I think you would save more energy letting inmates cut grass with push mowers.
In the case of the gas turbine you are only moving the pumping energy from the gas plant to the customer's turbine. "There ain't no free lunch".
