Peter Torr from the Visual Studio Tools for Office team recently expanded on my sandboxed AppDomain set of posts.  Peter adds some aditional code to change the code base of the AppDomain, which prevents untrusted addin types from sneaking into the FullTrust domain the original domain executes in.  He also adds my suggestion from the first post of adding evidence to the sandboxed domain.

Peter also pointed out that in v1.0, v1.1, and beta 1 of v2.0, SHA1 and MD5 objects are not serializable, meaning that if you modify the sample code I provided to create HashMembershipConditions instead of the strong name membership conditions it currently creates, you won't be able to set up the policy on the new domain from the old domain in the way that's shown in the sample.