Flattr creates a system where neither the giver nor the receiver knows how large a donation is until next month. That's not really a solution and it certainly isn't elegant.
Why is that a problem? Isn't the perception of a micropayment, such that it's an insignificant trifle? Why does the particular size of a trifle matter to the giver?
Also, why is a month's delay universally bad? I can see that it would be bad to some people, but there are certainly a lot of other content-creators for whom this wouldn't be a significant problem at all. Actually, I would think that a month's delay would tend to encourage content with at least some staying power.
It's not a solution for micropayments, in the vein that Radiohead's pay-what-you-want model isn't a solution for the music industry selling CDs.
But for casual content creators, the ability to buy a beer for a particularly well-written article or comic, this is excellent. It's a middle ground between ads and micropayments--better than ads, because you know people are rewarding you directly for enjoying your content, and you're not forcing advertising on them.
Plus, I think it can be argued that the better your output--the more it's linked to--the more you'll get paid. At least that much is predictable.
If you depend on it to pay your rent, you're going to need lots of people to click those buttons - and when lots of people do it you care less about how much each one gives and more about the averages. Flattr should publish "average pay per click" statistics, I suppose.
And I do think that it's an elegant solution that reduces the number of actions required to contribute to things you enjoy to a single click.
[edited to add]
Another way to think about it is that the variable is not the percentage of visitors that are willing to pay X dollars for your content, instead it's the average payment of the visitors that are willing to pay anything for you content.
I agree with you that these aren't micropayments in the strictest sense. But your argument seems to be along the lines that apples are a poor dietary choice because they're not oranges. A content creator gets paid something (likely in variable quantity comparable to a micropayment) with very little thought required on the part of the payor: What's not to like here?
