Jamie Zawinski: If you haven't seen
Google Maps yet, check it out: it's pretty impressive! If, like me, you're too lazy to read the source to figure out how they accomplished it, that's fine, because
this guy has posted an analysis. Short version: lots of transparent PNG overlays, and communication with the server by treating a hidden IFRAME as a socket.
[jwz] 12:21:51 AM Link Google It!