Attention! Phani on Deck!
One of the most common feature requests we hear for Astoria is the ability to mark properties on an entity as hidden. Currently in V1 we support this on the server, but not with the .NET or Silverlight clients.
Phani, resident Astoria hacker (and a really good tester), has written a very good post on how you can roll your own override of client serialization behavior to support this functionality with the v1 clients.