Invisibility
 

How can you make an object invisible when you render it but have it still cast shadowds and show up in reflections?

If anyone knows then thanks

i'm kinda interested in this as well...would it require some sort of compositing?

have a look at the shape node in attribute editor. open the Render Stats tab.

for shadows, couldn't you bake them for xcample?

Turn off Primary Visibility, under the Render stats in the
Attribute Editor when you have selected the object.
That should work :)