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.