Really cool talk. I've been thinking similarly, OSM now has such rich data that the blockiness of the default OSM Mapnik layer can be a bit restrictive to how well that data is communicated. That said, the default OSM Mapnik style is still the finest most widely deployed online cartography.

The image with the happy and sad faces can be found on John Krygier's blog at makingmaps.net/2009/06/12/cartominutiae-combined-symbols-on-maps/