Depends on what sort of permissions FB asks for on install.
My suspicion is that they'll want everything they can get their hands on (location at a minimum). Eventually, they're going to want to replace your phonebook, etc.
They definitely want to replace your phone book. Perhaps even your address book (take me to where Jon R's office - even Siri would balk b/c you likely would not have his office address in your addy book).
If the accuracy was high, these would be killer features for many people.
My suspicion is that they'll want everything they can get their hands on (location at a minimum). Eventually, they're going to want to replace your phonebook, etc.
The sad thing is, people will just let them.