Everyone of my ex girlfriends have friended me on Facebook. Neither me or my wife have a problem with it. We take our vows very seriously and have the utmost trust in each other. The rest falls nicely into place.
A few female friends from HS and later are friends on FB as well as my wife. I almost never hear from any of them. At least one I have to wonder why is still my friend, she is a hardcore 0 lover. Odds are she ignores my posts, what few I make.