I really like the north=snow, south=desert idea, but would it be possible to give the user more control over what general percentage the desert and snow take up? I like the way it works, but I personally would like a bigger desert in the south, for instance.
Edit: Also a couple more options for controlling spawn points would be nice, like what biomes to prefer for spawn points, and options for specifying single-spawn-point near town, far from town, etc.