I suggest you wait until the PR update is over. I also saw some changes in my site. Some times, PR increased, but then it decreased. But now, finally, PR of my sites seem to be stable.
My blog is new. I didn't sell links and blog posts. Just placed two banner ads and two blocks of AdSense Ads on the home page. The PR is zero and become PR4 when the update occurred 2 days ago. But when I checked the blog yesterday it's PR fell back to zero. I really have no idea why this happens, all I can do now is hope that it will turn to PR4 again next day.