An email from my hosting provider:

We are contacting you to inform you about some upcoming scheduled maintenance. To prevent power issues, we are moving your server to a different Network Rack. This will be performed on multiple servers and we will start it at 9AM CST on July 12th, 2012.
Estimated downtime for each server will be 20-30 minutes. Please note that this is being done just to avoid any major downtime due to power loss.