I like Android intents and all, but I think Facebook is misguided if their plan is to release a new version of Home every month. The intent preference is only remembered for the same version of the app... that means if they choose to update the version the user will be asked if they want to launch the intent with Facebook Home again ("Just Once" / "Always").
Facebook already knew this, that's one of the reasons why AT&T and HTC are included in this project, for HTC first device they will install it as system app which will avoid this problem.
Collaborating with HTC and AT&T allows them to install 'Home' as system app in future devices, this will allow their app to add 'layers' on top of any app. This can only be done if device is rooted or app is installed as system app.
You've got this problem (wether this behavior is an actual problem or a benefit to the user is open for debate) no matter what if you rely on being a default Intent in any way. What do you expect them to do, never update again?
