People (understandably) hate to register
It's unfortunate that signing up via Facebook or twitter or some other OAuth method gives people such a creepy feeling. It sure is a lot more convenient for everyone involved: don't need a password, no email confirmation, sometimes it's one click and you're in.I feel like Facebook screwed this up for everyone when people's feeds were covered with apps their friends were using. Now when a site asks you to authorize it with facebook, users don't feel like they can trust what it's going to do.