If you've been selling links on your site, chances are that your PR has been reset to N/A (grey toolbar PR). There are many changes happening at the moment and one of them is the dropping of PR on a massive scale due to algorithm update. Honest and genuine websites are not affected and you will see the PR is still the same while crappy sites which exist for the sole purpose of selling links have lost their PR. Has your PR turned grey (N/A) recently?
It's been happening on a large scale for about 2 years from what ive seen. But it's not the only reason that a site will lose pr.
Before it was only like big well known sites which were found to be selling links (having somebody reporting them etc) but now I think that the algorithm has got better in detecting sites which sell links. Hence many of the smaller sites are having their PR turned grey.
Buddy - well said except the time-scale you mentioned. Google started penalizing sites selling links in 1/2 September - 2007. http://www.linux.org/ -- the Official site of LINUX OS was a PR9 site - but being an Open Source project - it was generating Good funds through footer links sales -- YES - you guessed it right - from Gambling sites. Since, September - 2007, it is still PR5. Google has not penalized the domain to save its own skin - as if someone typed LINUX - and didn't find the official Page - Google would have looked like a FOOL - and its Search Algo would have been discredited by millions of users who do not have any connection with webmastering and only surf Google for information it provides. Google has since lost its credibility to webmasters - but not to a normal surfers -- It has penalized sites like - phpnuke.org (now PR5) www.forbes.com (PR5) can you imagine ??? winscp.net - was PR8 - penalized (became PR4) - now got its PR back. I have studied hundreds of authority sites (no site can be of more authority than LINU in the field of Linux software) -- and also small sites. Google could never penalize ( has no nerve) - to penalize an authority site of SERPs ( Here is the proof ) . Because - business ( read $$$ s means more to Big Boss G than other metrics ------ not matter what they say in public) as it has to save its own reputation - credibility. Its all about HYPOCRICY and nothing else. @ OP - it is nothing new really - it is just an strategy to control the web HEGEMONY really - and Google believes in MONOPOLY/Dictatorship.
Google has such a huge monopoly in search and stuff like pagerank. Sometimes I see very stupid sites with really high pagerank while other descent sites with a miserable PR. Google should redefine their logic of pagerank and focus on quality rather than how many links are you able to get from other sites.
I have 5 sites that pr disappeared on, these were sites with "advertise here" links. It is stupid that google is punishing web masters for making money (no biggie though just find advertisers privately)
Google is allowed to sell your links on other websites but you are not allowed to sell your links on other websites They given the "not related topic" argument but that doesn't cut it for 99% of the link sales. From relevancy pov, how is it different listing on a relevant category in a directory from displaying your link on related topic pages through google adwords ? You just have to acknowledge that anything google does is to increase their profits and because they are the biggest player you play by their rules or assume the risks