The 2nd presentation at next week's AJAX World is on AJAX Security.
After just coming back from MI 08 last week where Silverlight 2.0 was the hot topic, I've been thinking about the Silverlight security model. After all, anytime you install a binary extension to the browser there is a security consideration.
ActiveX was sort of all or nothing, Adobe Flash has had security challenges, Java Applets, Windows Forms browser controls, etc.
Shawn Farkas, who keeps a .NET Security log HERE has written several interesting entries on Silverlight security.
Here is a list for your enlightenment.
The Silverlight Security Model
Silverlight Security II: What Makes a Method Critical
Silverlight Security III: Inheritance
Silverlight Security Cheat Sheet