accessing form controls from other class (Real Challenge)

I agree. And if you want to go further in user-friendliness it's good that you run all time consuming non-UI operations in a separate thread to avoid UI freezings - experts say that a freeze longer than 30ms can be noticed by human perception. And when you use delegates and fire events between the forms and the logic classes it's so damn easy - just use the compiler-generated BeginInvoke and (eventually)EndInvoke methods.

Controls, and any other class fields don't have to be private or protected. It just breaks encapsulation if they're public, something most of us probably don't want to do. I would agree with stevenmjones. If you want one form to access another form's controls, it's better to raise events for the other form to handle. I believe that's the most conceptually correct way to do it.

I think controls in the form class are all private. You can only access within this class. If think you cant access this controls of the form but you can make a public property of that control so that you can access it anywhere esp if out on the namespace.

This is not something I would recomend doing. The good, right, and proper way to do something like this would be to have your other class raise events to allow your Form to update its own controls, and to have the Form invoke methods or set properties on the other class to update it with any changes in the controls. The general rule of thumb is that the parent should know everything about its children, but the children should not need to know much about their parents. Kind of like real life!