Originally Posted by piclarke
But the question is where does the recreational definition end and the commercial definition start.
In the U.S. it is pretty simple. If you require payment from people that you take on board (whether you call it a "contribution" or "sharing" or whatever else) then you are operating commercially and must have all the appropriate licenses, insurance, certifications, and so forth. If you ask people to share expenses, but will take them on board even if they do not make such a contribution, then you are not operating commercially.
Personally, if I pay then I am a passenger--I will act like a passenger, and I will expect to be treated like a passenger. If you want me to be a crew member then I will not pay you, and if this is an overnight passage then at the very least I expect you to provide me with meals and a berth.