I like the fact you can log in to LiveJournal.com using OpenID but most of all I love that you can leave comments using OpenID. OpenID is so far the best way to "sign" your comments, to prove that a comment is yours and does no belong to someone else using your name or nickname.
This is important for everyone, but in some cases it may be crucial -politicians for example. It makes the platform a safe place to be active (fake identities is a major non-starter for well known people that rely on their fame).
Using OpenID may be a bit geeky now, but services like Wordpress.com are starting to provide users with OpenID accounts for free -I know AOL is doing the same thing, Microsoft's InfoCards will make OpenID even more friendlier for Windows users (it is based on OpenID as far as I know).