Tony has a nice post on the joys and frustrations of teaching Valentinianism. Since he has opened the subject, I thought it would be fun to say a few words about it myself, since I teach this area all the time. I personally find the Valentinian mythology utterly fascinating, particularly how these Christians assumed a Platonic worldview, combined that with a cosmology they knew from the Sethian Gnostics, and reworked all to make it function within the Apostolic Christian tradition as the first complete systematic theology. And as Tony realizes through his wonderful classroom exercise (I think I'll try it too), they did this through exegesis of scriptures, Jewish and Christian alike, in the same was that other Alexandrian fathers did, especially Clement and Origen. When I teach Valentinus along with other fathers, it becomes soon clear that his system and that of his students is not very far removed from Origen in particular.
I usually start my lecture on the subject by saying to the students that I am going to tell them a story that never happened but everything in it is true (from the perspective of the Valentinian Christians that is). I also mention that the main concern of the myth is how this imperfect world of suffering is connected to a transcendent Good God. Or as Valentinus himself said in a letter, how our spirits can come to dwell in this "toilet" (he actually uses language I can't post!).
Then we go on to discover how Plato and Sethian mythology is recombined in a thoroughly Christian context, with the result that our first systematic Christian theology is born. Part of this systematic theology is the use of sacraments, and probably the development of a few additional sacramental practices. What do they do? Nothing less than release and protect the fallen spirit so that it can return home. Marriage as a sacrament is part of this process, and since the Valentinians thought that their own marriages were highly charged sexually in order to conceive children with the strongest spirits, well it is a fun time in class finally getting away from the obscene asceticism of so many of the early currents.