I can't imagine how complex the development of the UI must have been. Can you tell us a little bit about the technical implementation? What languages and frameworks you might have used, things that were particularly difficult?

Edit: looks like the client is hand-written with jQuery. I guess the next time someone makes a joke about jQuery you can send them this site. :D

Edit2: Just to preempt it, let's not have a debate about the state of JS frameworks here, there are enough of those already. :)