I asked this question on the official announcement post, but thought I'd get a faster and possibly better answer to the question here:
Isn’t this a violation of pretty much all SocNET’s TOSs? Granted, it will work if what you keep from your visitors is good enough, but still… Doesn’t seem right to me. Just wondering if folks might get themselves in a bit of trouble. ...After reviewing heaps of Facebook's various terms (finding several instances of this language) I've come to the conclusion that this DOES violate their terms.
IV. Application Integration Points
You must not incentivize users to use (or gate content behind the use of) Facebook social channels, or imply that an incentive is directly tied to the use of our channels.
Within the same document, Facebook goes on to say:
We can take enforcement action against you and any or all of your applications if we determine in our sole judgment that you or your application violates Facebook Platform Terms and Policies. Enforcement action is both automated and manual, and can include disabling your application, restricting you and your application’s access to Platform functionality, terminating our agreements with you, or any other action as we in our sole discretion deem appropriate.
I’m pretty sure everyone else covers this issue in about the same way, and the way this is written Facebook could not only kill the specific offending connection, but also all other connections you have with them, and even your account.