At the moment, the address box disappears when not being used, and is replaced with the domain and title of the current site. It reappears if you cmd-L or hover over the box.
I find this a bit annoying. I like to see the full URL at all times. Also, there is a bit of a delay when hovering over the box.
I suppose some people like the reduced visual clutter of having the box vanish, but I would like to be able to have the option to disable this behaviour.