My workhouse, Mid-2010, 17-inch MacBook Pro appears to be developing a video hardware problem: with increasing frequency the external video display randomly flashes black, and Expose' displays window icons instead of windows. I think the video driver is either corrupt or the adapter/memory may be on the verge of failing. Because I rely so much on this machine, it's prudent to be on the safe side. So the old MacBook Pro has been replaced by a new, 16GB RAM, 512GB SSD, 15-inch Retina MacBook Pro.
That's the good news.