Last time I looked into persona, it was essentially unusable for my usage - there's no reasonable way to use a different email address to sign up for every site. I like to know who leaked my email address when I start getting spammed.

Edit: looks like they may have have fixed it: http://support.mozilla.org/en-US/kb/how-do-i-manage-my-perso...

Though I'm not sure if it remains usable with hundreds of email addresses.