An article I worked on has recently been published on MSDN. The article, SharePoint Administrator's and Developer's Guide to Code Access Security, introduces CAS to SharePoint administrators & developers and then walks you through why it's important & relevant to SharePoint. Then I dig into how to trouble shoot, the different deployment options for custom code and finally how to create deploy custom CAS policies.
While the article is written for SharePoint 2007, everything applies to SharePoint 2010 as well.
SharePoint administrators and developers should have a strong working knowledge of .NET code access security and how to work with it in the context of custom SharePoint solutions. This article explains .NET code access security and why it is important to SharePoint administrators and developers. It then goes into the details of the different configuration options, advises on best practices in managing code access security in SharePoint environments and walks through a complex scenario.
Hope it ends up being a good reference for some folks!