In my ongoing quest to:
a) get my Facebook music annotation game "Herd It" running and
b) master all web technologies,
this week, I taught myself how to write AJAX apps.
XMLHttpRequest object sends requests to a server script (e.g., PHP)
Server responds with XML info
XMLHttpRequest updates to the DOM as it gets new info.
I've used this to integrate the iLike API as the music player for Herd It. Now I can play all the (30-second clips of) music we want and not get sued!