Update: Just in 1month Google again Updated PR Check PR Update April.
Seems like Google slapped websites involved in Buying and Selling links passing Pagerank in this PageRank update. I was aware about this fact and hence i already warned every one in my article Are Paid Links Evil in Real?. Seems like many sites getting slapped with a drop in PageRank.
Here is a list of some sites, including major publishers, Seems to have taken a hit overnight.
I am sure there are many more websites which are affected and slapped. Is this a direct hit by Google against sites that sell paid links?
If you are selling links on your website then i will suggest you to use Nofollow Tag . While selling links on your website !! That will not only save your rankings but also save the ranking of your advertiser !!
I had also seen some search engine optimization having some affective results for there clients.