Edit: I'm talking about the material tab preview, NOT the render preview. Here's an image of what it looks like on your screen. I think everyone can agree that it's ridiculous for this little image to be re-rendered every time you click that material. Hopefully, this image makes it clear exactly what I'm talking about when I say "Materials window with its Preview section".
Original question: When I'm jumping between objects in the project, if I happen to have the Materials window open with its Preview section expanded, Blender re-renders that material preview every time I switch objects - even if it's the exact same material. And even worse, the preview is never rendered to the same quality that the final project will be rendered to, so the preview isn't as good as it could be. The computer may render that same low-quality preview hundreds of times, always rendering the same ball or monkey head.
So is there any way to save this preview for a material that is shared between many objects? That would avoid the constant jumps in CPU usage, and maybe could allow Blender to efficiently render that preview in much higher quality. Even if it isn't saved between sessions, it would be useful to keep it in the memory cache.