I just tried it on the Times Crossword page. The workflow is really simple and elegant. I put in my email address. It took a second to determine there was no Persona account, then asked for me to create a password. After that, I clicked on an authorization link in my email account and as soon as I did that it immediately logged me in. I clicked Log out and back in again and it immediately recognized me and logged me…
It does seem a pretty elegant way to log in, the only concern i have is that it's kind of unclear what password i needed to use to login. I had already created a browserID password at some point in the past, so when i went to the times crossword and clicked sign in, i was prompted for a password. my first thought was maybe i had already signed up for the times crossword, so i tried the password i probably would have…
As far as the password, I thought it was pretty clear that the password they are asking for is your Persona password, but maybe that's because I had just signed up.
The point is that you'll only ever need one password, so it'll be great to be able to have one strong password rather than tens of weaker ones.
[1] http://identity.mozilla.com/post/32395255498/announcing-the-...