I think Hermes only pulls information from contacts you've already inputted into the n900. E.g. if I put my best friends name and phone # and girlfriend name and phone #, Hermes will only pull information for those two people from Facebook.

It won't pull all your Facebook contacts to your device (which would be somewhat unwanted behavior anyway consider I don't keep in contact with most of my Facebook friends anyway). But you could make it so you can select or deselect the contacts you want or don't want.