I was just messing around with a very simple file, and while I guess turning off and on a focus map slowed Rhino and the rest of my system to a crawl even though the task manager said it wasn't on average using more than one core(there seemed to be tiny intermittent spikes on the others.)
On reopening Rhino it seems the problem is in the render preview mode, everything was still bizarrely slow until I shut it off. Which is funny since I wouldn't have thought the render preview would care about the glossy reflection focus map.
V4 or V5?
I believe we're seeing some problems in this area in V5 too - we're dealing with it.
I have the same problem with Rhino 5 and Brazil 2.1 . I can not switch between some of materials in Material Editor. Could you tell me, when you could fix it?
I installed last release of Rhino 5.0 and Brazil 2.1 and nothing has changed. I still have the same problem with Material Editor. So it's very difficult to work this way. There is no problem with Rhino release 22.02.2012. Each later release has this bug.