tedster - 4:18 am on Feb 25, 2011 (gmt 0)
Here's some official word on the update:
Google's Official Blog:
in the last day or so we launched a pretty big algorithmic improvement to our ranking—a change that noticeably impacts 11.8% of our queries—and we wanted to let people know what's going on. This update is designed to reduce rankings for low-quality sites—sites which are low-value add for users, copy content from other websites or sites that are just not very useful.