Persona makes signing in easy for Gmail users
The problem with persona is that it sends the same identifier to all websites (nominally your email address).  That makes it super-easy for those websites to feed your activity to a central tracker like DoubleClick which will consolidate all usage information from all DoubleClick affiliated websites.<p>Persona would be a lot more privacy-preserving if it generated a unique identifier for each website.  A "persona" for each website instead of one persona for the entire interwebz.   Since the system is mostly automated it shouldn't be that hard to add one extra layer of indirection.<p>It might even be possible to shoe-horn it in to the current protocol with just a little bit extra on the browser and identity provider sides, but no change on the website code.<p>If anyone has actually done that, please post, I'd like to hear about it.  Availability of that functionality would sway me to start using Persona and probably anyone else who is worried about spreading their email adddress far and wide across the internet.