http://msdn.microsoft.com/en-us/library/system.runtime.serialization.datacontractserializer_members.aspx

So as it turns out, your XML stream must have the XML Nodes in Alphabetical Order when trying to deserialize XML data into an object.  Very wierd.

Many thanks to Einar Ingebrigsten!  I needed to serialize and deserialize some configuration data in one of my Silverlight projects I am currently working on.  This really came in handy:

http://www.ingebrigtsen.info/post/2008/11/29/Serialization-in-Silverlight.aspx

The executive summary is that you can use the DataContractSerializer without the need for DataContract or DataMember attributes.  Einar even gives you some sweet helper methods for Silverlight to make your life even easier.