Probably the most troubling of all of Facebook's new privacy options is the section on "What Your Friends Can Share About You".
If someone you have as a friend visits a site, Facebook will not only share their information with that site, but will also share your information with them.
For example, if they visit a greeting card site, it will remind them to wish you a happy birthday if its close to your birthday.
I've chosen to disable all of the items that can be shared. As much as I trust my friends on Facebook, I don't know what sites they are visiting.