Thought this was an interesting read:

http://thehairpin.com/2014/07/what-happened-when-we-gave-our-daughter-my-last-name

Since getting married I hyphenated my last name and we use that name when describing ourselves as a family. My LO has my last name as his middle name and my DH's last name as his last name. It'd be interesting to hear how folks decided on their LO's names.