This thread has been so interesting to me, and I appreciate both the candor and goodwill everyone has shown in expressing opinions.
Our DS is 11 and we (the three of us) still really treasure our family vacation time together. We see it as the time when we really focus on who we are as a family, on doing things that are important to us as a group and sharing the things that are important to each individual.
Maybe I'll be singing a different tune once I have a teenager, but -- said kindly and respectfully -- I just cannot imagine taking someone else along on a family vacation. We do lots of day-trip type things where we sometimes take one of DS' friends along, but I can't imagine that it would be anything other than incredibly difficult to manage having someone else's child along and figuring out how to both have a fun family vacation and work in another young person's wants/needs. Just deciding when and what to eat when I took one of DS' friends with us to a local waterpark last summer was challenging enough....
Maybe I'm talking like a typical parent of an only child who just doesn't know any better yet? But I guess my take, which I haven't seen here yet exactly, is that a 'family vacation' is just that.