For still photography, focus isn't a terribly hard problem to solve. Autofocus works, and DSLRs let you compose, focus, and shoot manually as well. Easy peasy.
On the other hand, for movies shot using large-format sensors, focus is a huge issue. The amount of work spent following focus on a movie is significant, and it fails more often than you might think. Modern lenses are incredibly sharp, but they have such a tiny range that is in perfect focus that they are hard to use. Admittedly, the people who use these cameras and lenses are professionals with years or decades of experience, and they do well... ...But -- if we could focus our shots after the fact, it would be a true game changer for movie making. We could chose just what part of the scene should be in focus, and change that throughout the shot easily. Yes, this moves yet another part of the movie making process into post, but that's not a bad thing. As other people have suggested at other fora, editing/coloring/framing and visual effects are all done in post, and it helps make better movies. This would help too. Having the depth maps automatically generated would make visual effects easier and better as well.
I recognize that the amount of processing that goes on to make these images makes a motion picture camera a challenge, and the number of high-end motion picture cameras is probably a tenth of a percent of the DSLRs that are made, at most. Still, we could just capture the 40 MRays and do the processing later; storage and networks are getting faster and larger all the time.
Come on, Lytro! Make it happen!