While changing a bug work item state to "Done" in the Microsoft Visual Studio Scrum 2.1 process template I noticed that the "Effort" field became invisible. I was quite happy with it thinking that there might be a new rule to make a field hidden. I checked the work item schema file and found that it is not a new rule but a new attribute to make a field hidden if it is read only and there is no value. Attribute name is: "HideReadOnlyEmptyFields". It is part of the "Layout" tag under the "Form" tag.
<Layout HideReadOnlyEmptyFields="true" HideControlBorders="true">
As you can see above another option is available for hiding the control borders. These are 2 new attributes added to TFS 2012 form layout. You can read more about the Layout available attributes here: Layout XML Element Reference.