This is an excellent plugin, I purchased it to upgrade the existing shadow catcher in Carrara 6 Pro.  This allows the use of global illumination with the shadow catcher not currently possible in Carrara 6 Pro.

This picture was rendered using the shader plus plugin with an HDRI image for lighting.  Below is a link to their website.

http://www.digitalcarversguild.com/plugin.php?ProductId=13