Database applications can be scaled up or out by using SQL Server Service Broker, which provides asynchronous messaging and queuing infrastructure. The great thing is that the framework of this functionality is already built into your existing databases! In this video, I explain the basics of how a Service Broker application works and the database objects behind creating your own Service Broker applications.
Video resources:
SqlDependency class
Service Broker samples on CodePlex
ssbdiagnose utility
Voluntary DBA 