DH and I each kept our own names, and we hyphenated DD's last name.  We thought a lot about it, but decided that if she was hyphenated, then both of our names would be in her name.  It seemed to us that it would maybe eliminate the confusion that comes with just one parent having a different name from the others in the family.  She's not quite 2, but she uses her whole name when someone asks her what her name is, "I'm Lucy X-Y," she says.  I think it's adorable, but no one else can understand what the hell she's talking about with that answer.  She refuses to use her middle name--perhaps adding in "Anne" is just one syllable too many for the little gal.