Google spent February and March making an example of people, and it is worth being specific about who. Text Link Ads, one of the larger paid-link brokers, got hit. A cluster of sites selling posts with embedded links got their PageRank visibly zeroed out in the toolbar, which is a cosmetic number nobody at Google particularly cares about but which functions as a public flogging everyone in the industry can see.
The message underneath the enforcement is the part that actually matters: a link Google decides was paid for, however that payment happened, does not count as a vote anymore. It might still send a visitor. It will not move a ranking.
For an industry that spent years treating link acquisition as a straightforward numbers game, that is a real shift, and I do not think it is finished playing out.
The honest version of this story is that Google is trying to solve a problem it created. PageRank made links valuable, links being valuable made a market for them, and now Google is spending real engineering effort trying to tell the difference between a link somebody paid for and a link somebody gave because the content earned it. That is a hard problem to solve algorithmically, and the current approach leans heavily on human reviewers acting on tips, which scales badly and looks arbitrary from the outside.
What I would watch is the nofollow debate running alongside this, because it is the same argument from a different angle. Some sites are experimenting with putting nofollow on their own internal navigation links to concentrate what people are calling “link equity” onto the pages that matter most, and Matt Cutts has been cagey in public about whether that actually works the way people think it does. My guess is it works today and stops working the moment Google decides it is being gamed, which is the pattern with every one of these tricks.
The practical advice underneath all of this has not changed as much as the enforcement has: write something people actually want to link to, and stop paying for the ones that do not earn it on their own. That was true before this crackdown too. It is just no longer optional.