What is OpenID?
If you’re confused, that’s understandable: OpenID is a little new, and will make more sense as an increasing number of sites on the web start to support it.
In a nutshell, OpenID lets you take your identity with you, proving to other sites on the web that you own a particular URL. LiveJournal’s OpenID support lets you use your LiveJournal identity (just your URL) on other websites which take OpenID, and also lets you take your non-LiveJournal identity and use it here.
What does this mean?
— leaving comments on other blog sites, and proving who you are
— being able to add/trust/ban people as friends who don’t have LiveJournal accounts
— off-site LJ utilities that require you to prove your identity
Also, claimID allows users to stake a (centralized) claim to all URLs, search results, del.icio.us bookmarks and other online artifacts that relate to them. In effect it’s like introducing yourself via your web presence (or, alternatively, clearing up any confusion about your identity.)
UPDATE: OpenID has a potential cure for Website password overload from C|Net’s Web 2.0 blog