Google Maps and XSL
This is in addition to the (now expected) XMLHttpRequest stuff. There even appears to be some of Microsoft’s weird VML, although as I’m on a Mac I don’t have access to IE/Windows to see what it’s doing with it.
As for Google Maps itself, it’s an amazing piece of work but it’s a shame they didn’t follow map.search.ch’s lead in degrading gracefully to a static version for unsupported browsers.
If anyone has any further insights in to how it all works, please post them in a comment.