Millions of blog publishers using Google's Blogger.com service were unable to use the service mid-afternoon Thursday (including Google itself). Service has since been restored after 20.5 hours of issues.
According to Google, during scheduled maintenance work Wednesday night, the service experienced some "data corruption" that impacted its behavior. As the near 24-hour long meltdown continued, bloggers and readers were experiencing a variety of anomalies including "intermittent outages, disappearing posts, and arriving at unintended blogs or error pages" according to the official announcement post.
Google did indicate that a small subset of Blogger users (estimated at 0.16%) may have encountered additional problems specific to their accounts. Yesterday Google rolled back to a pre-maintenance state/version of Blogger - from Wednesday May 2011 - and is currently restoring posts which may have been temporarily removed around that time. WM will provide more information as the story develops.
It will be difficult to determine just how much Web user traffic may have been diverted as a result of the downtime and service disruption. It does serve as a good reminder of the importance of creating and storing backups remotely and of having the ability to those deploy those backups quickly.