Here are three great videos to get you up to speed on SignalR
Building Real-Time Web Apps With SignalR
This talk was about SignalR 1.1, but the foundation applies.
Scaling the Real-Time Web with SignalR
About SignalR 2.0 and begins to explore performance and scalability.
Under the covers of SignalR
An on stage demonstration of building a SignalR-like framework. Great to understand how it works.