The forum posts span the entire screen width as intended. However, there's an entire screen width of whitespace if I attempt to scroll to the right. This only occurs on some pages. I strongly suspect it is related to threads with mod notes at the top. It doesn't affect usability, but it's pretty odd.
There is no Login button in the header on any page. Only Register appears. Is this because the overlaid login prompt doesn't work?
On the bright side, sidebars and other menus now function properly!