I ran into this when using SharePoint Designer to create a simple workflow.  When I went to deploy the workflow to my site, I got a bunch of errors that looked like this:

(0, 0) Type System.Workflow.ComponentModel.DependencyProperty, System.Workflow.ComponentModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 is not marked as authorized in the application configuration file.)

The solution is pretty simple:  Add a new authorizedType entry to the System.Workflow.ComponentModel.WorkflowCompiler section in the web.config for the type in question.  For the error above I needed to add:

<authorizedType Assembly=”System.Workflow.ComponentModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35″ Namespace=”System.Workflow.*” TypeName=”*” Authorized=”True” />

Kind of odd the System.Workflow types aren’t in there already, but I am running in a minimal trust mode.  Maybe it’s different for full.