[shantanubala]

Usability involves more than one target audience: it also has to be easy for developers to integrate.

BrowserID (Persona) took me minutes to implement. On a non-trivial project, it may take a couple hours. The beauty of this is the fact that it still works without built-in browser support. It's designed to be a forwards-compatible API that only becomes more usable with time.

Additionally, email is an excellent way to establish a user's identity, and the fact that it's designed around email makes it easy for a regular person to understand its authentication flow.

The problem with SSL is that it is an all-or-nothing technology. There's a chicken and egg problem: people won't make good UI for it until it's widely used, but people won't use it until it has a good UI. Persona provides an implementation of BrowserID that has a decent UI, and the user experience will only get better with time as more people use it. The chicken/egg problem is solved there, but two-way SSL right now is practically unusable for anyone who isn't very familiar with it (most people). Using an email address is very familiar, though.

[StavrosK]

I've forgone traditional auth in favor of Persona because there are just too many advantages. The user might already have an account, the flow is very good if they don't, it takes literally three minutes to integrate django-browserid (or whatever it's called now) versus skinning quite a few templates for all the login and reset forms, it saves the user from having to remember yet another password, etc etc.

I couldn't be happier with a signin solution. It even complements my legacy solution very well, you can see a demo at http://www.yourpane.com (click "Persona", never mind the email field.)