I know exactly what you mean! For years I felt that way - that my life was not taken seriously because I wasn't having children like everyone around me including all my cousins. I felt as if I was excluded from their "club."
But ya know, after almost nine years of marriage, their kids are in school, they've popped out a few more, and now I get comments from THEM about how envious they are of the vacations I take, or all of the other interests we can pursue since we're not tied down.
Part of it was changing MY attitude as well. I realized after a while that, even though I dislike children, I was feeling sorry for myself, but I had no reason to. I have a great life, and I can do so many things that parents only wish they could do. I'm not saying I'm superior, but that I have lots to be grateful for being childfree. I can talk about house projects, travel, charity functions, volunteer work, and I do NOT have to be ashamed or feel inferior because I choose not to have a kid.
Keep your chin up - if you present yourself to others as a responsible adult, pretty soon you'll notice that they'll treat you as you deserve. And if they don't, they can take a flying leap, right? <img src="/images/graemlins/wink.gif" alt="" />