Vijayâ€™s weblog has a good post on â€œUnit Testing Business Logic in .NET RIA Servicesâ€œ. Good read.
From my understanding RIA.NET is going to be CTP in July, however, with one of the core items being that RIA.NET will utilize the underlying ADO.NET Data Services (Astoria) protocol. I think this is a good move.
ADO.NET Data Services represents a REST approach to data services supporting IQueryable – (ie. Entity Framework, Linq to SQL, NHibernate Linq).
I look forward to seeing more out of RIA.NET.