Well, after realising (or even RIAlising if you like puns) that RIA services weren't cut out for non-Silverlight clients, I went searching for The Next Big Thing. Can't remember if I mentioned it, so I'll bore you by repeating it, but all of this investigation is for a big project I'm in that will need some sort of central data access point that can be used by all sorts of clients, most likely being WinForms, WPF (one of my colleagues is really excited about WPF), ASP.NET and Silverlight. Ideally, we want all of these to be able to use the same point of access for data, with the business logic behind that point of access.
RIA looked like the answer, but doesn't seem to play ball with anything other than Silverlight. So, I went looking at its big brother WCF. The idea was to build an end-to-end solution that had a WCF service on top of an entity framework model, and various clients consuming the service.
This posts describes my initial excitement, great disappointment and final happiness (so far) with consuming a WCF service in WinForms, ASP.NET and Silverlight.