Esoos - 9:09 pm on May 6, 2009 (gmt 0)

I'm seeing a big drop for pages which had run-of-site internal links (i.e. linked in the navigation from every page on the site). Just happened yesterday.

Not sure if that's THE characteristic that caused those pages to drop, but rankings for other pages on the site are holding steady. Could be a bit of an over-optimization/too-much-internal-linking issue, for this site at least.