It's not so much an invasion of privacy as it is a willingness of the suckers who are making Zuckerberg rich to post almost everything imaginable on his website.
And it never ceases to amaze me how people will lay bare their lives for all to see. Kind of reminds me of CB radio, where some people seemed to think that the only folks who could hear their conversation was themselves and the person they were talking to...
And there have been indications that the "criminal element" (which sometimes includes ones friends) use some of the postings to time break-ins. After all, if you're at Joe's Bar, you aren't home!