As I just found out, it seems that Worpdress and its Automated Upgrade feature may still have some kinks in it to work out.
As a part of the upgrade process, Wordpress drops a .maintenance in order to signify that the Blog is undergoing some changes, and presumably to stop access to the database and files [...]

There sometimes comes a time in a blog’s online life when it needs to find a new home.
Photo: josjos – CC
Whether it be changing to or from a personal blog to a professional blog, outgrowing a domain’s original purpose, or simply a face-lift – there are a number of common obstacles that you can [...]