According to a Slashdot article that I just read, the problems with Windows Search have been resolved, with no need for everyone to edit their registries.
The problem was, in fact, Bing. For reasons only known to Microsoft, the Windows Search functionality apparently uses the Bing backend – even for doing local searches. There was a service outage today, which caused the frustrating black screen to appear.
I still think it is pretty inexcusable. A core bit of OS functionality should not be at the mercy of whether or not some backend service is up and running. The online piece(s) of it might go down, but the local search functionality should still work! There is no excuse for the whole search window to render as nothing more than a solid black rectangle.