someone please tell me where I find this new feature… 
yeah same… not sure to understand…
Still on 3.5, but already up my Unity pro + ios pro licenses to 4 …
What I found so far about it :
Dunno what they mean but… 
WTF???
Yeah, I’ve been trying to figure this one out as well - I think I have the answer.
The realease notes say
Which leads to this:
So it basically looks like they now support custom inspectors for materials (like the already do for scripts and other MonoBehaviour classes).
I’m sure most people have been assuming that “Custom Material Editors” meant something more like a Unity-made shader editor*(like Strumpy’s). I was thrown off on this because of their mention of “The Shader Graph project” in ninja camp VII: http://blogs.unity3d.com/2012/12/07/three-ninja-camp-vii-projects-at-a-glimpse/
The important part is that you can now easily define shader keywords per material.
Which means you can write one shader, have a bunch of similar-but-conflicting functionality separated out between keyword preprocessor defines and then specify which one of those you want to use on a per-material level.
For more info and an example project jump here:
http://forum.unity3d.com/threads/174143-New-4-1-Graphics-Features
Oh thank you very much for all your answers now understand! 
I’m going to close this thread because there is a real one in the shaders section.