I remember jumpseating on Virgin America, SFO to SEA. Plane was full and it was going to be the jump seat. Positive space pilot walks up to the agent and asks if all non-revs got on board, agent says no. He says Ill take the jump to get one on. Agent answered, well they're a couple. So the other positive space guy came up and gave away his seat. What I thought was interesting was that the two guys, whom I had been talking with during the boarding process never looked my way.
I've also had it where a DL guy who booked the jumpseat opted to take a FA jumpseat to allow me the cockpit jumpseat. For the most part I have seen the latter scenario.