When primal and I got married I never really considered not taking his last name because it was easier than my maiden name for people to spell and pronounce. But then he told me wouldn't wear a wedding ring. He broke his ring finger years ago and it's kind of deformed, so he said a ring would make it hurt. I thought he should wear one anyway, so I said I wasn't going to change my last name if he wouldn't wear the ring. Several arguments later, my name is his and he's wearing that damn ring.
I think a family should all have the same last name to show solidarity. But making up a new one would also solve that problem, I just know primal would have never gone for it.
I had a professor in college who put her and her husbands' name together and made a new one that their whole family used. I thought that was pretty cool. Generally you don't find guys that progressive (except on TFP!).