[MatthewCampbell]

That's half true. It's all or nothing on first use, but you can revoke any non-required permissions later: http://www.facebook.com/settings/?tab=applications

[aditya]

You can't take back the data tha you already gave to the app, however. Revoking permissions prevents the app from accessing your info in the future, but it's sort of limited once you've already given that data to the app