What I don't get is that some sites get those messages even though they never arranged a backlink in their life - and they still are advised to "clean their backlinks."
Such sites have gone with a completely natural backlink profile, exactly as Google encourages. Now they are being asked to make new arrangements for something they never arranged in the first place. I know that many of the unnatural link notifications are on the money. In fact, many site owners have been surprised to discover that someone they hired or outsourced to did do some shady link building.
But it seem to me there are a number of false positives going on, too - and that factor is now distorting the nature of the web even further than the original PageRank algorithm did.