Apparently the download and payment figures I (and everyone else) have been commenting on were pulled out of the air by the people who published them. So we don’t know exactly how well the downloads of “In Rainbows” did.
But given that some people did pay for it, “In Rainbows” has paid better as downloads than it would have as a P2P leak. And I would re-iterate that unpaid downloads are comparable to promotional costs for CDs. So at worst this experiment has been something of a success and turned many eager fans into paying customers rather than copyright criminals.