I still have a funny feeling about the robustness of Persona. For instance - let's say one of my emails gets hacked, my crappy Yahoo email. Does that give them access to my other Persona accounts? Would I (or anyone else) be able to know if the account is compromised? Normally you change your password and that's the end of it, but I'm not sure what happens with Persona. What if my kid brother uses my computer - would…
No, it gives them access to whatever site you registered with your Yahoo! account. (EDIT: If you use the temporary bridge they implement, they could get access to your other accounts if they got access to the bridge. This won't happen if your email provider supports Persona natively).
> Would I (or anyone else) be able to know if the account is compromised?
Yahoo! probably would, and could tell you.
> Normally you change your password and that's the end of it, but I'm not sure what happens with Persona.
You change your password and that's the end of it.
> What if my kid brother uses my computer - wouldn't he have access to any site that allows Persona logins? How do you lock it down?
Just log out of your email provider.
Really, Persona is just a way to make your email provider your authenticator. It's "Facebook Connect" for your email provider.
Security-wise, if your email gets hacked, what happens is what would happen anyway, since almost every site can request a password reset by emailing you. The attacker has access to that anyway. Persona removes the hassle of remembering one password per account by letting the site ask your email provider if they know you.