As usual I waited for the 1st security update to start moving some of my bogs over to WordPress 2.5.
I updated the plugins, backedup the database, the theme files and uploads.
After carefully reading WordPress.org’s upgrade instructions I decided to install the plugin maintenance mode to display a splash saying the blog was undergoing maintenance.
After uploading all the necessary files, I tried to visit the upgrade page http://example.com/wordpress/wp-admin/upgrade.php and guess what the maintenance mode plugin would no longer allow me to access anything except the maintenance splash page.
So if this happens to you the solution is to delete the plugin from your plugin folder.
Now I just have to get used to the new dashboard and layout.