Playerprefs can only save basic variable data like float, int, bool, etc... For custom structures like GameObject's you need a serializing solution. (Someone correct me if there is a way to serialize GameObjects into playerprefs, i ended up doing it manually as an xml file)
I believe this is what Easy Save does, as well as other similar tools. I haven't used Easy Save myself, but from what I hear it seems to solve people's basic data saving issues altogether.