There are some heavy lag issues with the latest daily. They are already resolved, and will be available once Keymaster releases next daily.
As for the material updates, i think they should not be updating at all. At very least materials should not update, maps and their previews should not cause that many problems. The thing is that one should not really use material editor preview when using interactive, because either way, you always care about the end result, and you are tweaking end result when looking at interactive.
Why would you want to see shaderball when right in front of you, you can see how it's going to look right in the scene on final image? That applies for everything. I think previews only make sense when you render non-interactively, because when you run interactive, what you see in interactive VFB is always the most relevant, and it renders those shaderballs in material editor irrelevant. And of course it causes lag, because you are basically launching another rendering session while one is already running. For slate, there's an easy workaround, there's a button on the bottom left of the window that disabled thumbnail updating. I always disable it when working interactive.
It requires change of mindset of course. It's like with new Gmail - you always hate it first, but if you were to return to older version after getting used to new one, you would be probably angry a lot more. If you notice, many of the applications build around interactive rendering do not even have shaderballs, as it's expected you will always look at the end result anyway.
It would not be a problem if rendering those shaderballs was free. But rendering while rendering will always be at a cost of lag. And especially when drawing material previews doesn't bring much benefit, as described above, it's really not worth it. When you launch interactive rendering, your actual scene becomes your material preview. If you were to limit CPU usage, your thumbnails would generate faster, but your interactive preview would render slower, and since you mainly need to see how your material really looks in scene, not just on shaderball, you would actually lose some productivity, instead of gaining it.
