This is a very wordy multi-part post. I understand it's going to be too much reading for most, but I thought someone might find it somewhat useful, so here it is. Best of luck.
While the new Mental Ray rendering engine is a much needed and long overdue improvement for Revit, IMHO, its implementation into Revit shows a disconcerting recent tendency of the developers to flub new features. Furthermore, it has the fingerprints of Autodesk marketing all over it – an intentionally crippled rendering feature set. From what I understand, a limit of 4 cores for rendering, slower rendering speeds than Max, no photo backgrounds (you've got to edit an exported image using a third-party photo editor). The whole material dialog is a case study in poor UI design. Then there's the big kahuna – what we're here to talk about today – a completely botched material library system workflow.
Once you kids really dive into the material library, you might be shocked to learn that there's no easy way to store Render Appearance Materials (the Mental Ray shaders and/or textures – for brevity, I'm going to refer to them as MR Materials) for use in other projects. Custom material definitions reside within the project file, not within an external library, unlike previous versions of Revit. And there's one more subtle but very critical distinction – the MR Material is directly tied to the Revit Material.
The amount of work keeping this straight and using the various workarounds will prove to be a deal breaker for many, and will send users looking for alternatives – which is just what Autodesk is hoping for, since with the new FBX export, there's a very convenient workflow waiting in Max. See Marketing 101.
So, what's the problem?
First, it is rather awkward to share MR Materials with others, especially within an office setting or on the web. If you were hoping for some slick material file download sites like Maxwell and V-Ray have, where you can go to share and download materials, that's not readily in the cards since there's no such thing as a separate material file in Revit 2009. Also, no support for external shader plug-ins, etc. If you were hoping to have a neat material library on your office network, where everyone could share materials, that's not going to be an easy option either. There are some workarounds that we'll get to in a minute, but I know from experience how difficult it is to manage a shared library even under the old but easier AccuRender system. Throw in a few workarounds and hoops to jump through and the whole enterprise quickly falls apart.
Second, it's the workflow stupid. Here's where things get really complicated really fast. This is difficult to keep simple, and if you haven't already run into this issue, it may take a bit of a conceptual leap. The really big rub is: as it stands now, there's really no quick and easy way to change between custom MR Materials on a bunch of modeling elements. See, some users know exactly what the rendered materials are supposed to look like, and it's just a matter of tweaking those assigned MR Materials. I however use the rendering tool as a design tool – I often will try many different material and color palettes on a variety of modeling elements. If you're the former, this probably isn't as big an issue for you. If you're the latter, this presents a workflow stoppage...