I know people collect addresses from groups and blast direct messages inviting for an event or just to visit their fan pages or become friends. I don't think it's a way to go, spamming.
Commenting on pages and profiles doesn't work too. Posting to groups gives nothing.
Looks like there's no way for free traffic. But I'm not sure. May be I just haven't found a clue yet. Would you suggest me some method to get free Facebook traffic, please? Share anything you know. Twitter could be milked at no cost, what about the big F? Is it me or it's really impossible?