Approximations:
Google.com - down 10%
Google.co.uk - down 40%
Google.fr - down 33%
Google.de - down 25%
Google.co.jp - down 35%
Addressing whether this decline is seasonal, 2-year charts appear to show that this is mostly an unprecedented decline for Google. Their growth has been explosive in every market until recently and, in the US and UK, Google failed to experience really any seasonal dips in all of 2005. In the US, it's the first dip since pre-Holidays 2004 and in the UK, it's the first real dip in over 2 years. (other 2-yr charts aren't available)
On the flip-side, Yahoo.com (although, not a great comparison as it's much more diversified traffic - more content, less concentrated on search) appears to be flat across most of the last 2 years, but trending slightly down since the end of 2005, as well.
As I understand it - 'reach' is related to the number of page views and users for Google's domains... and is not tied to syndication partner traffic, traffic from Google to other destinations, and is not impacted by many of the issues discussed in the forum (i.e. Google pricing changes, relevancy, etc.)...
That said, are there any hypotheses as to why a peak occurred in late January/early February, or why a consistent decline has occurred since?
...Google having reported very strong Q1 revenues...
This doesn't necessarily have to do with more traffic... Google has been masterful in extracting revenue efficiently from existing traffic. i.e. better relevancy, higher minimum CPCs, smarter testing to increase CTRs, etc.