I have been having a good time watching these videos of one of my my favorite writers and developers Steven Sanderson . These videos are all about the new Asp.net 4 with Upshot, Knockout, WebApi and how they come together to make building Single page applications (SPA) faster and cleaner. The second video is about C#5 asynchronous operations and how this can be applied to web applications. The code to perform asynchronous calls to the database have been made less chunky and less complicated .Finally one also learns how asynchronous call work underneath and how duplex connection to the server are made and handled by SignalR. You can read this article Asynchronous scalable web applications with realtime persistent long running connections with SignalR.
Here are the links to the videos.
Goodluck and happy learning