Never. I don't have a Facebook account, but it'd be pretty naive of me to assume they don't have a profile on me as well, especially since they've already admitted doing so[1].
Assuming the Ghostery team has identified and coded in all the trackers they use (and that assumes Ghostery isn't actually spying on its own users, and selling that to FB - I don't think that's likely, but who knows?).
I don't know all their transactional email strategies, but I've noticed one is those "Do you know [name] or [name]" emails that try to coax you back onto Facebook by asking you if you know certain people and want to friend them.
