Have you followed nofollow (and how it has changed)? Graywolf puts nofollow in historical context, noting how current rants about paid reviews are causing Google to put their users last:
What’s really happening is we’ve got another FUD campaign going, this time designed to stamp out paid reviews in an inconsistent, arbitrary and undocumented manor. Some people are allowed to do it, some aren’t, and we don’t know why, rather than take a risk people will just decide not to participate, due to a lack of a clear answer. What happens then, the market goes underground, the disclaimer requirement fades away, and no one, especially the people viewing a page know what editorial forces might be at work behind the scenes influencing that page. Way to go Google and good job of putting the users needs ahead of your own!
When Matt Cutts uses nofollow on his own editorial links doesn't that invalidate nofollow? Why does Matt need to hoard PageRank when he is clearly against that practice? As Matt stated 5 years ago:
It's pretty easy to spot domains that are hoarding PageRank
Indeed it is.