If you are not already aware of them, you might be interested in a trio of third-party tools that can help you protect your privacy on Facebook.
Hopefully, why you should never trust Facebook is obvious by now. Perhaps you feel like you still need it, though -- or stubbornly refuse to believe it is really all that bad, whether because you think it is not much of a risk or just do not believe the evidence.
You may take all reasonable precautions, including using no personally identifiable or sensitive information in your account or profile data. Maybe you use a password and email address for the account that you use for nothing else, and refuse to communicate with anyone who actually knows any personally identifiable information or secrets about you on Facebook. Even so, there are risks.
Facebook clearly is not concerned with your privacy any more than the absolute minimum required to keep itself in business. There's no such thing as a trusted brand, but there is certainly such a thing as a brand that is thoroughly suspicious -- and Facebook seems to fit the description when it comes to personal privacy. Any time Facebook appears to care about your privacy, keep in mind that it took Congressional posturing to keep the corporation in line even to that small degree.
It is clear that even when Facebook offers something that looks like some kind of privacy protection, the offer is not a promise, and relying on it is a recipe for disappointment. With that in mind, the problem of protecting even the most minimal sense of privacy while using Facebook seems insurmountable. Thanks to the efforts of a number of hackers and entrepreneurs who actually care about privacy -- not only theirs, but that of others as well, even if only because it serves as a convenient business model -- there are some options that can help at least a little.
In no particular order:
Untangle offers the SaveFace bookmarklet, a script that can be saved as a bookmark in your browser. When you click a bookmarklet, it does "something" -- usually involving whatever page you happen to be visiting at that moment. In the case of SaveFace, you can visit your Facebook page then click on the bookmarklet to rest your privacy settings to Private. According to Untangle, it currently covers Contact Information; Search Settings; Friends, Tags, and Connections; and Personal Information and Posts.
A similar bookmarklet is offered by ReclaimPrivacy.org. Unlike SaveFace, the purpose of ReclaimPrivacy.org's tool is to scan your Facebook settings and detect certain types of privacy vulnerabilities in your account settings. In theory, at least, it should be more thorough than SaveFace -- but less automated as a means of protecting yourself.
3. Connect In Private
At ConnectInPrivate there is an annoying tablike thing floating over the left-hand side of the page. Take a closer look: it reads "Secure Your Facebook Profile". If you click on that, it takes you to a Facebook application that offers a fairly comprehensive Facebook privacy feature set. Of course, what it provides is little more than a convenience layer over manually adjusting your own Facebook privacy settings, but it can be used for free and, if you like that kind of thing, you might find it valuable.
A final word
Connect In Private has one definite advantage over the other tools, though: it is more actively maintained. As of this writing, ReclaimPrivacy.org's script is not compatible with current Facebook privacy settings, and there is a note on the page to that effect. SaveFace is far from a complete solution, for that matter. None of them are perfect, and there is always a risk if you trust your private data to a site like Facebook. Each of them might help a little, though.
In the end, I for one find it difficult to trust the Facebook application offered by Connect In Private. Your mileage may vary.