Maybe I am just old fashioned, but I think it's important to get to know each other's families. To echo some of the other sentiments, if I am in a long-term relationship, I definitely want to meet some of the family members, so I can see what I am getting myself into. Not that I think my family has to be BFF with my future husband's family, but they should at least meet/mingle/get to know one another.
And you never know these days...
