EDIT by Stym: updated to 1.4.5 beta build... so far so good. Thanks for your patience, all. The 1.4.4 clients are compatible with 1.4.5
The server is empty, and I think the reason is that many players are playing on 1.4.4, the server is not updated to 1.4.4 (YET!). We will update when all plugins (or the most important ones) are stable enough and the recommended build of bukkit for 1.4.4 comes out.
If you want to play, follow these instructions from Flandyn:
You could restore your minecraft folder, or download minecraft for 1.4.2. When you are updating it doesn't mean it is impossible to join.
How to restore your folder:
Press Windows button -> Write this in the search section %Appdata% -> Go to roaming -> Then right click your minecraft folder -> Go to properties -> Then hit earlier versions -> Wait a few second and you will see the options -> Go the the date you updated your minecraft or before -> Then restore.
I hope that this would help you.
If this doesn't work, download this program MCNostalgia and follow his (sonicrules) instructions on the post.