Okay, I should have done this in the first place but here is what I found when I did a google search:
Having its roots in Southern tradition, the grooms cake has been around for quite some time and is making a fashionable comeback on the wedding scene.
Traditionally, a grooms cake was sliced and boxed for the unmarried girls attending the wedding to take home and place under their pillows in hopes that the man they dreamed of would be their future husband. Grooms Cake has come along way since then. Today the cake is meant to be a reflection of the grooms interests, whether it be one of his hobbies, favorite sport, alma mater,profession, etc..
Its a personal choice when to serve the cake - either at the rehearsal dinner, as an alternate dessert with the wedding cake, or as a late night dessert for the wedding party. Just because primarily groom cakes tend to be a fruit cake or a chocolate cake shouldnt dictate what the bride and groom should have. Obviously being named "Grooms Cake" it should be a flavor and theme that the groom enjoys.
I guess I was on the right track...