Currently in APIv3 the most recently added layer ends up on top.

It would be great if an order or zindex property was added to each of the following objects, that controls which layers show up on top of which:
google.maps.KmlLayerOptions
google.maps.FusionTablesLayerOptions
google.maps.visualization.MapDataLayerOptions 


This would be a big win for http://maps.eyesontheforest.or.id/ . The page has a number of wide-area base layers that should be fixed at the bottom, plus smaller polygon layers (species distributions) that should always stay on top, and year-by-year deforestation series that should be stacked in chronological order (no matter the order that someone visiting the page actually adds individual layers onto the map).
Currently have a workaround in place that hides "higher" layers temporarily when something new is added, then puts them back in the right order after a short delay (about 700ms works most of the time..but it's not ideal).

This would presumably be a win on Google's servers as well, since all enabled layers get rendered into the same PNG tiles to be loaded on the map - with only one single possible layer order there will be fewer possible files to generate and cache under mt[01].googleapis.com/mapslt.