On the question of an IBL being able to cast shadows, bagginsbill has stated that, yes, it can produce a shadow. I was skeptical but tried it and it is true. IBL can cast a shadow. I didn't find the shadow very satisfactory, so I have turned shadows off for the HDRI lights that I'm creating.

"A lonely climber walks a tightrope to where dreams are born and never die!" - Billy Thorpe, song: Edge of Madness, album: East of Eden's Gate

Weapons of choice:

Poser Pro 2012, SR2, Paintshop Pro 8