This doesn't work anymore?
http://www.runsaturday.com/RSS/ActivityRSS.aspx?ActivityId=42882
in particular:

[InvalidOperationException: Unable to generate a temporary class (result=1).
error CS0200: Property or indexer 'SlodgeRoutesTools.ChartPoint.Course_OriginalPolylineIndex' cannot be assigned to -- it is read only
error CS0200: Property or indexer 'SlodgeRoutesTools.ChartPoint.Course_OriginalPointIndex' cannot be assigned to -- it is read only
]
System.Xml.Serialization.Compiler.Compile(Assembly parent, String ns, XmlSerializerCompilerParameters xmlParameters, Evidence evidence) +1010
System.Xml.Serialization.TempAssembly.GenerateAssembly(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, Evidence evidence, XmlSerializerCompilerParameters parameters, Assembly assembly, Hashtable assemblies) +1902
System.Xml.Serialization.TempAssembly..ctor(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence) +74
System.Xml.Serialization.XmlSerializer.GenerateTempAssembly(XmlMapping xmlMapping, Type type, String defaultNamespace) +105
System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace) +489
System.Xml.Serialization.XmlSerializer..ctor(Type type) +6
RSS_ActivityRSS.GenerateFeed(Int32 viewingUserId) +477
SlodgeRoutesTools.RSS.BaseRSSPage.DoPageLoad(Object sender, EventArgs e) in C:\Users\Stuart\Documents\Visual Studio 2010\Projects\DNN\SlodgeRoutesTools\RSS\BaseRSSPage.cs:21
SlodgeRoutesTools.RSS.BaseSyndicationPage.Page_Load(Object sender, EventArgs e) in C:\Users\Stuart\Documents\Visual Studio 2010\Projects\DNN\SlodgeRoutesTools\RSS\BaseSyndicationPage.cs:14
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
System.Web.UI.Control.OnLoad(EventArgs e) +99
System.Web.UI.Control.LoadRecursive() +50
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

Instead the JSON version is ok.
http://www.runsaturday.com/RSS/ActivityJSON.aspx?ActivityId=42882

Hi Stuart,
I'm "thinking" of using it and the XML interface would be easier for me to deal with since I already deal with .tcx files which are pretty similar to your output. If it's not a big deal...

jon