google cleaning up the yard

paid directories could be easily found, they all have the 'powered by x script' feature so if google just checks for that in the source, they could easily detect sites engaging in link trading. They could find the link directory, but that doesn't mean sites in there are willingly participating in black hat techniques or what google considers black hat.

 

It's taking time. They started the crusade against paid links in 2005

 

In my opinion this entire paid link crusade is just a smoke screen. Of course, some paid links are easily identifiable but if you do it in a clever way google will always have some doubts. In addition, what is on the top of Google search results - paid links (sold by Google). They may not pass any PR juice but surely they will bring you traffic - and that's what having a website is all about. People care about PR just because this may give them an edge in the SERP's, but once you on the top, you care only about staying there.
Google sells links whether they like it or not.They can't have the same monopoly in this business as they have in the search engine industry.
The paid links debate is blown out of proportions!!!

Google wants you to use nofollow tags for sites that you don't fully trust. Hell! I don't even trust Microsoft. So who am I going to link to? Answer: freakin' adsense

Webmasters have no choice and they will buy links because that's their freakin' right to buy any type of advertising they like and Mr. Google will not tell 'em what to do.

Personally, Google is employing a scare tactics, hoping that a vast number of people will stop buying or selling links, so they could stabilize their serps. Screw that Mr. Page & Sergej Schwartzkopf ! They want us to do their job for them now instead of working on a more intelligent algo. But that's just me huble opinion