When doing some modeling in Designer, create an error state - for example create a foreign key relationship with one side missing. You will get the error in the Message Log stating the error, but also a visual on the table in the model as well as the model in project view (red Xs).

Please support a mouseover affect - i.e. if I mouseover the table (where the red X is) I would see the error. Same thing for the project explorer view. This would be more consistant with development in Eclipse