The fb privacy settings allow you to restrict access to your content by other members, however, as a site, facebook can do pretty much anything it wants including resell any information/content/pics you put on their site to any third parties. That’s why it usually gets a pretty dismal rating when it comes to end-user trust of the website. It’s all in their sign-up agreement which of course, none of us take the time to read.
Re: GS, only select admins have access, and they don’t have time to snoop around PMs and private blogs. It’s only in instances where a problem/issue is reported that they have this option available to resolve these issues. Again, it’s a trust issue… one can be paranoid or laxed about these things based on one’s predilections, experiences, and of course hearsay.