privacy and the law
Beware of legal issues about privacy.
EU privacy regulations are usually much stricter, giving more protection to customers. In general, you are not allowed to ask personal information, unless you *really* need it, and even then, you have to register your database with some regulating body (at least, that's the case in Belgium)
US privacy regulations on the other hand, hardly exist and/or are hardly enforced. That's just my experience as a rightponder... 👻