Flattr makes sense in so many ways, it won’t be long before many “appreciation” systems like Digg follow suite because, the Free Culture movement is really not about being anti-Money. Rather, FOSS is all about removing the primitive element of coercion, aggression and violence from the world economic system.
As we move towards true post-scarcity money becomes just another way to show gratitude. Remember the time when it was just an abstract means of exchange for the pre-Industrial, pre-Net age — an abstraction which existed only to drive people away from acts of altruism while enslaving their fellow human beings with Copyright and Intellectual Property Laws?
Flattr is in beta right now, but you can request to join as a beta tester.