Why did you decide to use Facebook authentication? Do you have plans for symbiosis with Facebook? Why have the user create a Facebook account instead of account in your startup?
We actually had our own authentication initially, but later decided to use Facebook Connect. We are using some part of data and features available on FB to provide core functionality, e.g. we use friends list for access control, we send SMS and email reminders through FB. We publish short stories on your activity on your wall (if allowed). And we have plans to put more social features, utilizing FB infrastructure.
Many people already have FB accounts, so we decided not to ask people to fill in all these fields one more time.