I can't remember which thread people were talking about log in issues, but I just noticed a few things and thought I'd share to see if they matched anyone else's problem.
I'm using Firefox 2.0 at home and work. Up until yesterday, I used the CF-Blue skin. At work, I go to the site typing chessforums.org (no WWW, no bookmark). At home I use a bookmark. In both cases, the forum didn't log me in until I entered one of the subs.
Last night, I switched to the Navy Blue skin at home. Today at work, I threw the WWW into the address bar for some reason and I'm logged in immediately.
I doubt the skin did it (since that's checked after I log in), but rather the way I get to the site. My bookmark at home is probably without the WWW as well, so once I update that I'm guessing I'll log in automatically there, too.
Hope that helps anyone else having trouble logging in when they hit the site.
ADD: It's the lack of www- going to chessforums.org leaves me not logged in.