If you are using their DNS service.
578 karma · joined June 12, 2011
http://www.informationweek.com/byte/howto/personal-tech/desk...
With the process you described, it would be really easy for apps to simply use another app's id. So, it seems that Facebook has implemented additional measures to prevent this. (e.g. using bundle ID and iTunes app store ID for iPhone apps)
Also, Facebook published iOS SDK that required secret key, but has since updated it to remove that requirement.
As far as I know, a lot of iPhone apps are shipped with App key and secret key. (For example, an open source project for sharing requires you to put your app's secret key: http://getsharekit.com/)