The current identifier is just working on the active layer.
A plug-in called 'DrillDown' is identifying all all layers and shows the result in a tree view.
I think we should merge the two tools and make an identifier that will work with all layers.
Perhaps excluding fields will be helpful. Of course these excludes fields need to be saved in the project file.
Combining this feature with the table editor will also exclude these fields in the table editor.
When a shapefile is loaded and it has excluded fields they can also be not loaded, increasing the performance.
When adding a layer using the new 'Add layer' routine (http://mapwindow4.codeplex.com/discussions/277940) the user can already select the fields it is not interested in.