I agree - I don't use a password manager, but I find this to be the best option. I would suggest using email vs having the user create a username (email is always unique, but when you have a common name and your username is sometimes taken, you have to choose a secondary or tertiary username, which can get confusing).

I don't have any problems wit Facebook/Twitter logins, but I would suggest holding back on the permissions requests. If I see that a website wants to have the ability to post as me or invite friends as me, etc., I will think twice about accepting. If they just want to access my name/email for auth reasons, I'm usually happy to do so.

I like OpenID, but am not sure if it is as widespread among the average user (especially vs Facebook or Twitter) an having that as the only login option may shy people away a bit.

Haven't used BrowserID, so personally I wouldn't use it. I don't know the numbers on this one, but you may get a specific demographic of users if you go with this one.