The other is an ultra-lightweight Wordpress plugin that embeds a linkpurl link tag for auto-discovery (so bookmarking agents can detect and grab the persistent URL rather than the impersistent URL up in the addressbar).
Based on a discussion in #code4lib earlier today, I realize that there are a lot of important questions, not to mention serious doubts, about persistent identifiers. I flip-flop on their utility myself, so I found the discussion very useful. (Thanks, edsu!) Maybe I’ll write a post or two about persistent identifiers to flesh my thoughts out.