kabz, a couple of things you said caught my eye.
On which pages does pressing tab not take you from the username field to the password field? I just tried it in a couple of places and it works for me.
What is the problem with Private Messaging? If you click Private Message next to any user's post you get a form. Type in the body of your message and click send. That's it.
If pprune is not behaving in the way I've described perhaps it is a browser problem? What browser are you using?