I am seeing a nice number of reports that signal the onset of a Google update being rolled out.
There are reports in the ongoing WebmasterWorld thread and tons and tons of threads in Google Webmaster Tools from webmasters claiming their sites no longer rank in Google. I just linked to several of them, but there are plenty more.
Thanks for letting us know about the problem with your site. I let the engineers know about the issue and they're going to take a look.
He did not respond that the site has issues or that Google fluctuates or that Google has algorithms that look for quality content. He responded that he will let the engineers look at this issues.
Is this related? I don't think so.
Most of the chatter I am seeing about an update comes from sometime this morning throughout right now.
A WebmasterWorld has a preferred member saying, "Seeing some significant changes today."
Is an update about to be announced by Google? Is it Penguin, Panda or something else? I'll keep you posted on what I find.
The last official Google update confirmed by Google was Panda #24 on January 22nd.
Forum discussion at WebmasterWorld & dozens of Google Webmaster Help threads (links above).