Even iray has no customized shaders, iray has a shader. It is mia_material (Arch&Design in 3dsmax) only. Actually, it is a shader that has mia_material interface and the implementation is different from mental ray (only for iray). mental images explains this is for the users who already know the mia_material. Such user doesn't need to learn the iray shader from the scratch. Therefore, some of the physically meaningless parameters of mia_material are disabled. They also said that they will support more physical shaders, like BRDF shaders. Someone asked about volume shaders support at the confenence, but, unfortunately, iray version 1 doesn't support volume shaders and will be supported in the following versions sometime.
As for a DCC software user, the problem of iray is they can use it from 3dsmax/Maya/XSI or not. But NVidia's explanation is 'that is autodesk's decision.' Although, mental ray 3.8+ standalone or NVidia RealityServer support iray. (See mental images web, www.mentalimages.com)
But I found another possibility, Bunkspeed Shot: Bunkspeed iray demo. http://www.youtube.com/watch?v=t5cn4UNqBfY
In my case, it is possible to use mental ray standalone, I would like to use iray via mental ray 3.8+.
In this blog, I will explain how to use mental ray standalone from 3dsmax. (Maya is similar anyway.)
This is basically useful for render farm users (only). But, if iray did not supported by 3dsmax/Maya/XSI, it might be useful.