There was an issue with the bottom login boxes not working which I was able to reproduce. The shoutbox cookie was (again) conflicting with the forum cookies. I'd forgotten to override that when I reinstalled it, but it's done now. Please let me know if that login breaks again, or if there is any other trouble with logins. Except for Jess at work. That doesn't count.
If all else fails with logins, you should always try to first delete all your cookies as well as make sure that you don't just refresh the forum page, but actually close and open the window again. This is because once you start browsing the forums it will often put sid=589hag98qtrhqw498gh or some other jibberish in the URL. SID means session ID. Your session ID is how the forums remember who you are. This is also what goes in the cookie, and it's what causes most conflicts.