I've created some proof-of-concept KML tiles for Google Earth (and hopefully other KML-aware applications). Open http://lists.openstreetmap.org/pipermail/talk/attachments/20080611/031b2ce7/attachment.kml to give it a try and let me know what you think. More info at http://lists.openstreetmap.org/pipermail/talk/2008-June/027159.html.