I was surprised account duplication wasn't mentioned as a disadvantage. If a user taps the wrong button on their tablet, then they can end up with one or more duplicate accounts if the e-mails are different.

I currently have an e-mail confirmation screen that makes it clear a new account is about to be created. I seem to remember Stack Overflow getting me to click a button too. It adds no real burden to new (non-Twitter) users.

I'm still wondering about the best way to handle this in Rails though. Passing the OAuth hash data through a second request to confirm the e-mail doesn't feel quite right to me, even if I make an OAuth service object to clean up the code and some policies to standardise the hash.