Great post by James Michael Hare I came across about using Sets in .Net. Definitely worth taking a look.
Very recently, building multi-tier application involving Silverlight front-end inter-operating with WCF back-end, I encountered very odd, yet annoying behaviour of Visual Studio 2010. I was building new functionality using Telerik RadMap for Silverlight control that was to display some spartial data supplied by WCF service. To achieve this my Silverlight application had to reference few Telerik assemblies (Telerik.Windows.Controls.DataVisualization.dll). What is important is fact, that Service Reference for WCF service had been there already, project built and everything was working nicely, until I added extra method to WCF. After using “Update Service Reference” VS command, I started getting following error.
Lack of further details with regards to this error and appropriate feedback from Visual Studio certainly does not help to get to the bottom of the problem, however after some investigation it turned out that one of Telerik assemblies caused this problem. When VS2010 creates service reference, default settings are that it should “reuse” all available types in reference. Excluding certain types from serialization allows service reference to be added successfully.
I hope this helps anybody who got stuck with this problem.