After listening to your explorminate interview I thought I might just mention that I consider MP to be something I'll try after everything's all locked down far later in the game dev/evolution.
It was a bit depressing to hear that it was ~30% of your dev budget and <0.5% of people have even ever clicked the MP button at all (I, for one, have not). But I do feel like this may turn out to be a core feature later.. That being said, MP wasn't high up on my personal wish-list for GC3 way back when the features were being hammered out... but I AM looking fwd to doing it some day...
cheers,