I have heard from someone that it is not possible to remove Facebook integration on your phone without resetting the device back to factory settings. That being said, if I go into settings->email+accounts and tap and hold Facebook, there is an option to delete the account. What actually happens if I do that?
If you tap "delete" it will delete the the account. What you can't remove (without resetting) is the Live ID linked to your phone. That might be what the person was talking about.