Well this has happened awhile ago now but Facebook changed there privacy settings and policy. There are many issues such as things that use to be closed are now open such as your likes and hobbies. But also Facebook has partnered with sites such as Microsoft and Pandora in what they call instant personalization were it adds your friends and music likes to the sites. But Facebook also makes these settings hard to configure with lots of settings and sub settings. There are much more issues as well which can be found all over the place but Wikipedia sums it up very well.