It's one thing to use the friend graph to show in your app who else uses it. That's pretty legit. The other use case is to store it to some database and keep it

It's one thing to use the friend graph to show in your app who else uses it. That's pretty legit. The other use case is to store it to some database and keep it there. FB provides since ~10 years widgets for showing who else is liking xy. I know these Social Widgets are not so customizable and thus not pretty enough to match some custom design but at least they provide some safety nets. Maybe Facebook could just provide more Social Widgets/CSS customizability instead of letting people write their own "Facebook Extensions".