Let's just say someone has a one-way ticket SFO-LHR. They do not want to fly, but the flight is full, so "volunteers" may be asked to change flights. Can you get bumped and then not fly at all that day and use the value of your original ticket towards another flight?

Even if your ticket is non-refundable, you can use its fare basis value toward a future itinerary minus what is probably the usual $75 ticket change fee. You don't have to count on the flight being full and volunteering to be bumped. Are you asking if you can have your cake (use the value of ticket in the future) and eat it (get bumping compensation vouchers) too?

Theoretically, if you have a refundable ticket, get bumped, and then don't take the new flight, you can get your original ticket refunded. However, the actual mechanics of the procedure could be very tricky. It will vary from airline to airline.

If you have an e-ticket, once you check in, the computer will show that the ticket has been used and you may have a problem getting a refund processed. If you have a paper ticket, some airlines collect the ticket itself when you check in and give you a boarding pass in exchange. You would need to retrieve the original ticket in order to get the refund. If the airline simply staples the boarding pass to the ticket and then collects the ticket when you board, you should be ok, since you still have the ticket. Then all you would need to do is submit the ticket for a refund.

And do it quickly. I ran into a problem where I had already checked in and the flight was delayed for 8 hours (UA, of course). I bolted for Southwest and was only a couple hours late.

Once you've checked in on an e-ticket and consequently do not fly, you have a certain window of 24 or 48 hours before your monies go to never-never land.