I stumbled across this post using the ASP.NET Ajax AnimationExtender to move points around and immediately recognised the similarities to the Silverlight 'race simulator' demos I've been playing with.
It seemed a natural progression to try animating same North Head (Sydney) race runner data using ASP.NET AJAX to animate the runner markers. A quick massage of the Silverlight XAML (using Excel!) and I had a couple of JSON arrays ready to go.
The result, as you can see, is not quite as smooth as Silverlight - and I suspect that Ajax would have even more trouble than Silverlight with 400 elements to animate!
View Sourceof the AJAX page - it's all there.