Gift Economies have been around for a while.
Most often the gift is not monetary but reputation/karma enhancing. I read Cory Doctorow's Book Down and Out in the Magic Kingdom when it was syndicated on his website. You can download it for free at this link. A highly recommended read.
He described a society that used Whuffies to recognize a persons reputational status in a post-scarcity economy to encourage the production of useful and creative stuff.
Came across a great instance of a gift economy on Twitter today. Its called Twollar
So you want to recognize someone for the value that they have freely offered to your Twitter community you send them Twollars by creating an entry like "Give 10 Twollars to @ggatin for telling me about gift economies" Twollars picks up the code and registers exchanges in their system.
The idea is that corporations will provide sponsorship so that Twollars will be translated in to charitable giving for worthy projects like drilling water wells in 3rd world countries.
I love it. Anything to break out of the corporate mindset, that everything of worth can only be measured black ink in by the bottom right hand corner of a spreadsheet.
So here is the deal. I will send a Twollar to any Tweeter who comments on this post. Heck of a deal. I have no idea how much this will cost me, I guess I should figure out how to the check the stats on this blog. Entirely likely that I will get off pretty cheap. Still trying to figure out the rate of exchange between Twollars and Whuffies.