[ricklepick]

This is not totally accruate.

Yes, you still have to deal with migrations. When you change the data model, you have to compensate, either with modifying the underlying data or by compensating for it in code.

"denormalization" is really just structuring your data model for best performance for your underlying data store and code algorithms. And you most certainly have to do this in mongodb as well.

The great thing about using migrations is you pay this price once, at upgrade time. Not in yoru code on every query to the data layer.