This rate is way over nearly every service out there, including Paypal.
Peter Sunde Kolmisoppi claims to be a socialist on the page here: http://flattr.com/team . I guess the outrageous fee that they charge shouldn't come as a surprise...this is what socialist governments do.
Silencing your opposition won't make it go away.
Typical behavior-driven ranking features (impression vs. click-through, length of time a user is on the site, number of times visited) can be simulated with clever enough bots, relatively inexpensively.
On the other hand, flattr has is not only a record of websites viewed, but an actual amount of money must change hands and is a powerful feature for the social proof of a website.
Granted, maybe there is a sense in which this makes it easier for spammers (just throw a bunch of money at it via flattr and you'll rank higher!) and they'll undoubtedly have to deal with spam like everyone else. But all in all I think this is a clever move and no one (in my knowledge) has tied social cash so directly to ranking.
