Casting call is interesting because it allows the Corp to use one of their agendas to openly taunt the runner. Although two tags wont completely deter most runners, Combining Casting call is probably best applied to already taxing agendas.
Agendas like Fetal AI, NAPD Contract, TGTBT,Explode-a-palooza or Award Bait, can become extremely devestating. The runner is forced to choose between letting the corp score or take a painful, and possibly game ending, tempo hit.
The second place I expect Casting Call to get played is in Wayland decks. There is obvious synergy between Casting Call and the new 'install faceup' agendas ( Underway Renovation , Oaktown Renovation , Hollywood Renovation). Since these agendas need to be installed face up anyways, and Wayland excels at punishing the runner once tagged (Dedicated Response Team, Scorched Earth), there's very little reason not to splash a Casting Call or two.