Just checked a couple of keywords we're monitoring and it would appear there has been a bit of a change. Since the last one we've been moving all over the place mainly lower page 1 but position 1 has changed hands again between our competitors. Maybe a result of whatever new filter has been applied...
Lots of websites have been affected, especially the ones that had some portions of copied contents from other sources. This is one reason why certain article directories have lost lots of previously indexed pages. Many sites have achieved better ranks, to the surprise of their owners because of unique contents on them. I also have noticed the update in PR but the overall web positions have not moved that much.
Google plan to have a major update every 3 months at least for a couple of years as they seem to think that SERP quality has been improving for the short tail keywords...the long tail key phrases still throw a bit too much irrelevant results...