How do non-developers get involved in the iteration rhythm? How does a business or UI person have all the answers on the first day of the sprint when developers need them? This is a great problem and people learning scrum seem to evolve through different levels over time.
This was the point to Karl Scotland's MMF post, and he did a great job of modeling it for easy digestion.
I commented on the sprint boundaries in general and my experiences through this process in other teams and how it was predicted by our agile coaches at the time.