I was going to work on that, actually. It's funkier than you described. If you clear all your cookies, then log in to
www.ninjette.org, if you go to ninjette.org afterwards, your login cookie will work (on IE, at least). if you do it at ninjette.org first, if you go to
www.ninjette.org, it will require you to login again.
Some of it is vBulletin weirdness rather than standard domain/subdomain weirdness, but it all will get ironed out at some point. Will likely push everything to the www. for consistency.