BTW, not sure if it's related but the 2am drop in traffic coincided with an error in processing our sitemap files. (Our sitemaps have been fine for over a year with no problems.) The error appears to be on Google's side. It reads: "We experienced a temporary error processing your Sitemap. Please try again later. To help us prevent these errors in the future, please post your Sitemap URL and the date and time of the error to our discussion forum. "