I had not heard of persona.org until the announcement that it's shutting down. 

I think it's an interesting idea. 

The browser is a good place to do identity. 

If the browser also did persistent cloud-based storage, beyond the 5MB offered by localStorage, we'd have an amazing platform, without adding much complexity to the JavaScript developer environment. 

PS: To be sure I hadn't written about it, I did a search. :-)