There’s been a lot of news recently about Facebook and privacy. My advice is simple: don’t assume anything you post on Facebook is ever actually private between you and your friends. If you assume that everything could one day be made public you’ll never have cause to be surprised.
Additional advice regarding tracking cookies: Delete any stored facebook.com cookies and only use your browser “incognito” or “private browsing” mode to access facebook. Logging out is apparently not sufficient to prevent tracking information being sent to facebook when you visit third party sites. See: http://nikcub-cache.appspot.com/logging-out-of-facebook-is-not-enough
Or, if this is still unpalatable to you, simply delete your account and stop using facebook and/or consider blocking it completely by adding a 127.0.0.1 address for facebook.com to your hosts file.