Flattr is the kind of idea that sounds great, that people love talking about - if only they could make a small donation to every website they liked - but that doesn't work because people are fundamentally too selfish. This is why ads are the only viable business model for a kind of "ephemeral website" - something you visit only briefly, derive some short knowledge or pleasure from until you follow a link somewhere el…
But thinking about, maybe the lack of a social component and some virtual rewards would have been beneficial. But I guess, after the first fail, nobody cared anymore for it, and they somehow failed to find their market.