I almost never use the Sherlock application that ships with Mac OS X, but if I find myself in a U.S. city wondering what movies are playing nearby, it is one of the easiest ways to find out.
I fired it up this evening and found that all the channels seemed to be missing. An empty window – even less inspiring than some of the movies on offer at the moment.
If this happens to you, go to ~/Library/Caches/Sherlock and delete what you find there, then empty the Trash. That fixed it for me. Elementary, my dear…. oh, never mind.