For those wanting to know more about Persona, check out https://login.persona.org/about
also since Persona is from Mozilla, you can see all the code and development and you know that privacy and user safety are number one priority.
https://rachelbythebay.com/store/ - just put this up yesterday - easy enough.
http://scanner.rachelbythebay.com/main - this one's been using Persona since it was called browserid. (Hit the gear on a call to see the login prompt - you only need the login for certain extended functions)
Click the "Log In" button at the top to see the Persona login screen.
http://www.deadmansswitch.net/account/login/ (click "BrowserID login", my UX isn't great).
http://www.yourpane.com/ (click Persona without entering an email address, my UX isn't great).
If you're making something, please please add Persona to the list of login methods. If you're currently using emails for logins, it's even backwards-compatible.