My app is broken into several assemblies. I'm sure I need to set a reference to the Enterprise (ES) namespace in my main EXE (were AppMain is and were the ES data source will be set). I'm pretty sure I'll need to set it in the assembly that contains my BOs. Any were else?

Actually, you only need to reference the MicroFour StrataFrame Enterprise Client.dll assembly from the main .exe (or whereever you set the data source).  Everywhere else can just reference MicroFour StrataFrame Base.dll because they won't care that it's an EnterpriseDataSourceItem... only that it's some type of DbDataSourceItem (the base class).

Cool