Open ID is a new technology that allows you to use one set of login credentials to access many sites. This is good because you don't have to remember yet another password or go through yet another Web 2.0 community registration process.
Simon Willison wrote a simple, clear explanation on how to turn your blog in to an OpenID. I followed his instructions, and now
http://www.saltycrane.com/ is my new Open ID! I look forward to putting it to good use. (In case you're wondering, yes, I am planning to add Open ID support to this site. Mr. Willison has also written a django-openid library to "enable your Django application to act as an OpenID consumer".)