FDO, Shapefiles and ArcGIS
For existing Autodesk Map 3D users the ability to read and write Shapefiles is a useful feature, likewise the access to simple feature layers stored in ArcSDE using FDO. You can even add to that working with WMS map services served up by ArcGIS Server that are similar to the Map Service capability of ArcGIS for AutoCAD, but without the ability to identify features.
If you use Civil 3D the included Autodesk Map 3D functionality gives you access to Shapefiles and ArcSDE simple features you can use in the process of design.
If the main reason I use Autodesk Map 3D is to read and write Shapefiles to work with ArcGIS than I'd say there is an easier way. ArcGIS for AutoCAD working with plain AutoCAD files is superior to using tools that read and write Shapefiles, simply because the support in ArcGIS of the resultant AutoCAD files is better. Namely the attributed feature classes inside AutoCAD files that are created and read by ArcGIS for AutoCAD and ArcGIS desktop are self-contained in the AutoCAD file and can include curves and annotation. The simple features in Shapefiles don’t support annotation or curves. Software that reads and writes Shapefiles in AutoCAD adds another level of cost and complexity; ArcGIS for AutoCAD is free and works on pure AutoCAD entities within a single AutoCAD file. But if I have Civil 3D it’s not a bad way to go.
When considering the Autodesk Map 3D FDO connector for editing however, I must be concerned not only about the lack of curve and annotation support, but also in the fact that the GIS data in ArcSDE may be participating in a geodatabase, for which the ArcSDE API used by FDO has no awareness. The blind simple features edits of FDO made directly to ArcSDE can and will ignore important data integrity rules established in a geodatabase, so be careful.
The girls are now 1-0 in the pre-season.