I have tried a simple mvc application that can be used to share photos between friends which gets updated instantaneously. An user connected to the website can upload a photo which will be automatically broadcasted to all clients connected at that point.
Here is how it looks:-
Latest version of source is available at photowebpro.codeplex.com
SignalR is an asynchronous signaling library for ASP.NET that can be used to build real-time multi-user web application. There is a simple and interesting video available on Channel 9 about SignalR, which will give you a heads-up.
Technology presumes there's just one right way to do things and there never is. ~Robert M. Pirsig