Welcome to vBulletin 4 - please post bugs here!
I've upgraded our forums to the latest version of vBulletin, 4.1.3. As part of the process, I had to migrate the existing style to the vBulletin 4 system as well as tweak some other settings. This means that there are likely to be things that are really ugly, or that don't work at all. Please post any bugs or other issues you see here, and I will look into them.
This is a pretty big change from the backend, as the style system is completely different. It should provide a good foundation going forward to be on the latest version of the forum software.
A few of the notable features are better smartphone integration (I'm still looking into how to get this working) and the ability for users to sign up with Facebook connect. I'm sure there are lots of small changes here and there as well.
There are still some issues to be tweaked--for example, I need to re-add the code tag checker. I really want to make this a vBulletin plugin so that I can avoid hand-editing the JS files every time a new version of the forum comes out, so it may be a few days before this gets implemented.