To take Ron's side for a change, I remember being offered reimbursement for the fuel I expended flying Angle Flights in support of Katrina and Rita. I turned it down, just as I turn down offers to chip in for gas money when I take non-pilot friends on 100 dollar burger runs.
I'm not real worried about the FAA MRAP vehicle crashing through my front door at 3am, disgorging a squad of body armored FSDO agents, and seizing my logbook and bank statements.
I'm more concerned about what I imagine to be increased civil liability should anything go wrong on a flight which involved the exchange of money.