Listening to Jeff Richter talk about Application Domain and Remoting.  He's a good presenter, and very fun to listen to!  Lot's of energy, but more importantly, very knowledgeable!  I have a weakness for low level computer details (compiler details, behind the scenes optimizations, etc), and Jeff has tons of great nuggets!  For instance, the ThreadAbortException is rethrown by the runtime, even if it is caught!  In order to stop this, you need to call the ResetAbort() method, which requires certain permissions.  Great use!  This allows us to load possibly malicious code into an app domain with restricted permission, then any malicious code can't swallow an aborted thread, and continue to consume resources.  Cool.  See?  Neat stuff!  If you haven't seen Richter speak, or read one of his books, I recommend it!