http://openid.net/
I'm opening this thread because
Jeremy's LQWiki-OpenID announcement is being overwhelmed by questions about the potential security issues. I'm not sure this is the correct forum, but I trust that can be addressed if it's desirable.
OpenID is an open source replacement for Microsoft's failed "passport" concept. It is fairly new and, as such, security is an issue. On the other hand, it has captured the imagination of a lot of high level developers for whom such a universal login technique would be extremely valuable.
My general advice to people who are concerned that someone might get their password and take advantage of it somehow is this. Consider what your OpenID password is protecting. Right now, it's generally the privilege to post on forums at which you are not registered. That's not really high level stuff.
Don't use the same password for your OpenID identity that you use for your bank account, or your root login, or anything that guards critical information.
My own position is that this idea is a great area for development, and I want to encourage it. Personally, my rule of thumb for the time being is that I will register at no more discussion sites unless they allow that registration via OpenID.