For those who don't spend their free time reading and listening to security and open source bloggers, you might not know what OpenID is all about. At it's simplest, it's a system for a distributed identity system.
What is a distributed identity system? It's the ability to ask the proper source if this person has access to this identity. Identity doesn't proove that this is a person, group of people, my cat or a bot. All it can do is proove that some requestor should be associated with this identity.
So what's new? You already have a distributed identity. However it's not tied together at all, (unless your username is unique enough to never be taken) so nobody would ever realize that this guy on Slashdot is that guy on delicious. It's protected by 50 different passwords. And there isn't any sort of way to say if you want to know more about me then go here. OpenID has all that. One password properly protects your access to all OpenID enabled sites, and since your OpenID is tied to your own blog, there's always a reference pointing back to you. That reference is something you own or trust somebody to maintain for you, taking more control of your own identity back for yourself.
In OpenID, identities are URIs. I can be qedi.videntity.org, infornography.ca, or sad_mcemopants.livejournal.com (if I had that login, which surprisngly doesn't exist). Which makes sense from a blogger perspective. You are your URI anyway.
So once you go to some site that allows you to log in with OpenID, you can throw in your blog URI. Then, some backend magic happens and some site talks to your blog, and determines your identity provider (which could be your blogging software, something you've written youself, or some other provider you want to trust) and sends you there. You log in with your idendity provider, and determine what information you want to give or deny some site. After all, it may be useful to let some site in on one of your secrets, like your location or contact information, if you think it is useful, and this way you don't have to enter it in yet again. Your provider will then pass that on, and you'll be identified with your blog URI to some site.
It makes things a lot simpler, especially with more and more people coming on board with OpenID. AOL has made your AIM id into an OpenId for you to use if you want. Microsoft has pledged support. LiveJournal, Wordpress and a whole lot of others already provide one to use. Sites are just beginning to utilize it. Technorati, Zoomr, and Imageshack with more to follow.