I think many people are loosing their PR even though there is no real massive PR update.. Have you lost your PR before few days or today ? I lost my 3 sites PR before 5 days. they are PR0 now Is PR toolbar working for you ?
+REP for the loss..... But, I'm rather tired of the Pagerank posts, people need to be worried about SERPs and not Pagerank. I'm assuming since you didn't mention it your SERPs stayed the same, which is great, nothing bad really happened. All you did was lose a number, a number that really means nothing. Unless you sell text links, then you should get penalized, since text links actually manipulate search engine results. If you think they don't then your very mistaken, your outbound link is still counted and anchor text taken into effect, which means it gives weight to that site for that keyword\phrase. So if someone buys enough text links effectively they can buy there ranking, which is wrong.
the way I observe it, PR is being monitored from time to time. Google is focusing on sites that sell links and penalizing it of course. PR dropping I should say. its not actually the official PR update but Google seems to have this site surfing. and when they found out that a certain site sells a link, Google thinks that its all because of the usage of the PR.(well, in most cases, PR is the basis in selling links.)