The reason I am not using Facebook anymore is because they have removed too many privacy settings.
- Your friends list is visible to everyone.
- Your group and page memberships are visible to everyone.
- You cannot block Facebook activity from appearing on your wall.
- You cannot prevent strangers from friending you.
These things would be ok in Twitter - because things have always been public, but not in Facebook.
This Valleywag article gives a good explanation of it.