I also really like how the birds flew in and I thought that it's one of the things people always said couldn't be done without Java or Flash plugins. By that metric html5 really is a success.
Although I wouldn't say there's a best part. The experience were running smoothly on my system, so it all the pieces added up to something more. Tough the draw/write were a bit out of place, but I can imagine that they wouldn't want to leave it out because of the way stuff you made (the drawing) interacted with the automated stuff (the birds).
I always run my browser un-maximised at only about 1/3 of my monitor's size, so I like how the web-experience came out of the browser, but like others, fearing a bit that this might become more normal. I already hate how youtube videos are auto-starting; imagine some tab in the background spawning multiple windows simply because they are trying to make an experience.
So if nothing else this shows that we don't need Flash even for flashy experience-oriented art sites :)
Yeah, the birds was quite striking. It reminded of a similar effort that was written in Processing by Robert Hodgin. http://www.flight404.com/blog/?p=81 If I recall, certain parts of Processing was ported to javascript for the express purpose of animating HTML canvas.
I especially liked how the birds flew in and rested on the drawn lines.
Also, this is a fantastic album.