I see a potential revenue stream for StackExchange and a great feature for users. There have been a couple cases where I felt so happy after a person answered my question that I would spend $5, $10, $15 to send them a gift.
What if SE partnered with product or service companies (per SE site) to make this feature possible.
It could be done completely securely with SE as the broker, with SE receiving a commission for each transaction of course.
It's a chance for SE to pay for its developers by monetizing the compulsive behavior of people who just had their day, week or project made thanks to a question answered. Completely optional and unadvertised. When the user makes an Answer they could be prompted, "feeling generous? send a gift...".
Food for thought... :-)
[Edit] Removed a point I made about adding a gift as a bounty... I agree this is the wrong direction.