"The tradeoff is that you have be disciplined in your data entry process...i.e. unique identifiers have to be spelled consistently, as you don't have the ability to enforce constraints or enumeration"

This is a really good point and one I should have included (I wrote the piece above). There is no easy way to validate syntax and spelling in the spreadsheet and we would often find ourselves hunting around, trying to find the typo that was breaking a particular project. We obviously got better at avoiding this situation as time went on, but it made the learning curve all the more difficult for new users.