Software: Blender version 2.70a
After a series of tests, adding a shadow catcher in Blender is easy with the Blender Internal as my default renderer–without the need of node compositing. Here’s the sample rendered in Blender Internal with an added effect of defocus node for my viewing pleasure :p.
Using the same model (again), with a HDR file as my environment, I added a mesh plane for the shadow catcher.
1. Select the mesh plane, check the ‘Shadows Only’ on the material.
Optional: The ‘Receive Transparent’ are for textures with transparency (pngs)
2. For the environment: Click the World tab then go to Texture. Add, change the clouds type to image, then upload the hdr file
3. Change the coordinates to ‘Equirectangular,’ and the influence to ‘Horizon.’
4. Back to the World setting, enable the Real Sky