Dave Hendricks posted an interesting article on ClickZ titled "Owned Data, Paid Succes", in which he talks about the risks associated with using data gathering via social sign-in on your website.
From the article:
Bringing owned data into paid media channels - sometimes referred to as data-onboarding - will revolutionize marketing like nothing seen before the invention of the Internet. But if you do not have rights to use "your" data in third-party channels, you are going to miss out on a big piece of the next big thing in interactive marketing: CRM retargeting.
You might ask, "How is my file not my owned data? I can email it. I can drop cookies on it and retarget it. I can even send terrestrial mail to it. That sounds like it's mine."
The data you collect via social signup is yours...to some extent.