Women's Lib vs. the Post Office
Here's a reason to consolidate last names when getting married: the US Postal Service doesn't recognized you as being related unless you have the same last names. Since both my wife and I kept our own last names after getting married, it was a bit of a hassle picking up a package for her today at the local post office. I even brought a bank statement showing both of our names listed at the same address. That wasn't good enough, though, since our last names are different. Better safe than sorry, I suppose, since I could really be an evil roommate trying to steal the brand new bread knife she ordered. (Of course, I could be an evil roommate with the same last name and still steal her mail, but better some safegaurds than none, I suppose.)
Luckily, my wife is also in the Army and I have a military I.D. card that states that I belong to her. That was good enough for the USPS, and I successfully returned from my mission with the package underarm. I don't think her I.D. card has any reference to me, though, so she still wouldn't have an easy time picking up a package addressed to me.
The lesson here? Marry a soldier. Or better yet, somehow end up with the same last name as your spouse when you get married.