How to get back in to your Wordpress site after a failed upgrade.

Wordpress update failed? Locked-out of your site. Maintenance Mode..

Delete the file called ".maintenance" (Note the dot)
It'll be in the root of your wordpress install.
That's it.

To get to this file, you'll have to either use your FTP program, or the File manager in your control panel (CPanel, PLESK, etc).