I'd like to use my Facebook account for my OpenID accounts. How can I do this?
Facebook uses OAuth, while Google, Yahoo, AOL, and MySpace use OpenID.
For sites that only accept OpenID, you won't be able to use Facebook. Many sites accept both OpenID as well as Facebook, Twitter, LinkedIn, Windows LiveID, etc., that are other non-OpenID solutions.
If you're looking to add support for all these ID systems on your website, you might want to check out Janrain's Engage.
As far as I know, Facebook allows you to log in to it using another provider's OpenID account, but doesn't actually create an OpenID account for you to log in to other sites. Does that make sense?
See this Facebook Developer Blog Post for some more information.