I made a mistake when creating a table, and setup a field as an int instead of varchar. I then used the scaffold dev tool to create the controller, model & views for the table. It took me a while to figure out why I kept getting "username is required" when submitting the form. Wouldn't it be better if the error produced said something about an incorrect data type?
FWIW, I tested adding "int" as a filter on my username field in the createAction method of the UsersController and it still just says "username is required".
Just a thought. =)