You might be wondering why the sudden drop in PR for a lot of the websites out there. This drop is the most serious PageRank Penalty I've seen so far.

The sites that are mainly affected are the ones that are selling links. Matt Cutts has been vocal about their opinion about paid links and thus now, it seems that they've finally updated their algorithms and put penalties on such sites.

Here are the top reads regarding this issue.

seomoz.com
http://www.seroundtable.com/
http://andybeard.eu
http://www.dailyblogtips.com
http://forums.digitalpoint.com/

I hope google reverse this changes as this has a major impact on the profitability of websites.