Most people now have a rough idea of how to secure their Facebook profiles at this stage. Or at least have an awareness of what is publicly available versus what is available to people in their friends list.
But many aren't aware of the risks of playing games and quizzes to not only their data but the data of those of whom they're connected.
When you add a game or application to your profile you potentially agree to allow that the same access as one of your friends to the developers of that game, quiz or application. The problem is you have no idea who they are or what they're going to do with data mined from your profile be it pictures or personal information. It could be used for marketing information, republished elsewhere or even result in identification theft.
Each application is not a single person you are sharing with, it is an unknown number which could range from zero to entirely publicly accessible. In your Facebook application settings, it defaults to "recently used" but that does not take account of all the games/applications/quizzes you have authorized to have full access to your data in your profile. Click this link whilst logged into Facebook to see the "allowed" apps in your own profile:
You may be shocked at the amount of things authorised that you weren't even aware were there.
Then remove (using the clickable "X") any games or quizzes you no longer actively use or trust. Also be aware of the "Edit Settings" on each listed. Some will allow individual privacy settings as exceptions to other things in your profile which you can change from "Everyone" to "Friends only" or whatever you deem appropiate.
The other key thing I want to write about here is that when you add an application or game to your profile you are potentially opening up not only your own data to strangers but potentially that of people connected with you.