I saw a CV yesterday that made me think about the purpose of having a Curriculum Vitae to begin with. This CV was by an established academic with a career of several decades at American universities. It included the usual information: work history, publications, awards, classes taught, and so on. The heading included his birthplace, marital status, and number of children. This last bit of data didn't raise any red flags for me but I don't think it's common practice in the US. Europe is a different story.
This is a dry subject. It's tax-form-typography, accounting-spreadsheet-debugging dull. I won't make any apologies for it. When the bulk of our interactions with society take the form of visits to social network profiles, though, it's helpful to remember the CV (or résumé) as the canonical form of self-description. It doesn't describe who you are as a human but it lists what you've done and alludes to what you could do next, given the right opportunity. Any modern social network serves much the same function in a smaller capacity.
So, let's assume you're searching for a job. You've submitted your CV to some people who may want to know more about you. Let's assume these people aren't myopic enough to search out your most unflattering Facebook photos but they'll certainly scratch the easily-Googleable surface. Should your CV already include the most obvious information? I've heard suggestions about how providing family background serves as an employer filter - those who actively discriminate against married candidates may not be conducive to family life - but some personal data isn't as simple as "married, two kids, born in Seattle".
I'm in favor of having personal data emerge organically. It's preferable to the alternatives. As some fields get more competitive, though, I won't be surprised to see usual hiring processes get more data-intensive.