Update: Matt Mullenweg responded to our email.
"The cause of the outage was a very unfortunate code change that overwrote some key options in the options table for a number of blogs. We brought the site down to prevent damage and have been bringing blogs back after we've verified that they're 100% okay."
The WordPress.com hosted service, which carries about 10 million blogs, experienced an outage in February. That outage was blamed on a data routing issue.
WordPress.com is run from three data centers, in Chicago, San Antonio, Dallas, with 1,300 servers between them, up from three servers in 2005.