[callahad]

I'd respectfully disagree. User testing generally shows a pretty strong aversion to and misunderstanding of Facebook Connect. Here's one such study: http://www.guanotronic.com/~serge/papers/chi13a.pdf

More pragmatically:

1. Do you mind that your users may get locked out of your product for violating Facebook's real name or one-account-only policies?

2. Do you really want to phone home to a publicly-traded advertising company every time someone logs into your site?

3. Social auth asks users to make a significant trust decision before they can even begin to engage with your product. Are you OK with that friction?

Passwords are a pain in the ass, but there are alternatives without the downsides and centralization of social auth. I personally work on Mozilla Persona (https://persona.org), and I'm more than happy to personally help out anyone interested in exploring it for their project. My contact info is in my profile.