I just finished implementing the IUpdatable interface[:)]
With ADO.NET Data Services, in the client part, you can use some LINQ queries which will be translated to an url. It’s really great to be able to use LINQ. However, this query is restrictive. For example, extension methods defined in the Queryable class aren’t allowed with ADO.NET Data Services (NotSupportedException).
When you add a web reference to your service, you will have some entity classes generated from the service metadata. If you have a relationship defined with a List<T>, or IEnumerable<T>, etc., in the server, the client generated code will use a System.Collections.ObjectModel.Collection. This class has a Count property. But when you want to use this on a LINQ query, you have a DataServiceQueryException. My ADO.NET Data Services Hooking POC solves it. [:)]