Revit, for some time has had the ability to export both 2D and 3D models to other CAD packages such as AutoCAD and Bentley MicroStation. The major issue when exporting the CAD information was that Revit would only use the primary category and ignored the sub categories when mapping to layers.
(Old Export Layers Dialog box from Revit Structure 2010)
For example, you can now configure Revit Structure 2012 Floor to output objects on the following layer. Notice that you can use modifiers on the layer names.
In the above example, I have used a simple material modifier to separate steel and column framing. You will have to freeze layers in AutoCAD to control the visibility as many structural items such as steel beams are output as blocks rather than simple line work.
This is definitely a major step forward and will help anyone who has to deliver a Revit model in DWG or DGN format.