A few more reference points to add to this thread:

• Google opened up a thread in their Google Webmaster Central help forum titled Think you're affected by the recent algorithm change? Post here.  huge bunch of responses, you can compare your situation with the hundreds of case studies listed

• There definitely were some 'goodies' whacked in this update, hence the Cult of Mac website getting whacked and then getting reinstated: http://www.cultofmac.com/crisis-over-google-has-reinstated-cult-of-mac/84362

• Australia has not been hit by the update yet, AFAIK. We're bracing ourselves on our network and watching for changes

I wish Google would release 'patch notes' for each algo change. Any competitive gamer will understand what I mean - most competitive games have balance tweaks where it is essential to release patch notes

For example:

Panda Update 1.12 (released 04/03/2011)

• Fixed a bug where high karma websites with low external inbound links were downrated in Panda Update 1.11
• Increased brand authority factor to 20% from 15%
• Google Adwords background changed from pink to yellow
• etc etc

One can dream...