From Simon Fell #:
IBuySpy is still labeled as demonstrating best practices, ouch don't think so. An interesting demo yes, best practices, don't see any. YMMV.
You're right, and the reason is that IBuySpy was never intended to be more than a feature demonstration for .NET. Though the parts are written acceptably, as a whole I've heard from at least one source inside MS that it was never intended as a reference architecture. The "best practices" label is certainly out of place.
For reference architectures, people should head to Microsoft's Patterns and Practices site. Not only does it have a ton to say about Design Patterns and Best Practices, it contains a bunch of well-designed apps with awesome documentation.