Having mused on this for a few days, I'm tempted to say that we should each pick a sub-genre that we're most interested in exploring - likely therefore within the major genres of pop, rock, or jazz - vet it with the group, and run with it. Keeping in mind you'll potentially have to play 20 tracks over the course of the night, so the genre would have to have some depth / breadth, while also still being a true, containable sub-set of the major genre. How does everyone feel about that?