The Lytro camera lets you take a photograph and then focus it.

"The Lytro camera [has] a special sensor called a microlens array, which puts the equivalent of many lenses into a small space.... [It has] sophisticated software that lets a viewer switch points of focus.... '[Photographs] become interactive, living pictures,' [Ren] Ng said. He thinks a popular use may be families and friends roaming through different perspectives on pictures of, say, vacations and parties posted on Facebook (Lytro will have a Facebook app)."

Digital cameras already let you see what part of the image is the focus point, but you don't always have time to look at the display, and in bright light it may be hard to see. Also, when you get your images uploaded into the computer and start to work with them, you might see details that you'd like to crop and focus on, perhaps things that you didn't even realize were in the shot... like in the movie "Blow-Up," when David Hemmings sees what may be evidence of murder in the blurry background shrubberies photographed with a film camera. I can't find the scene where he's blowing up the blowups of the blowups, so here's the scene with The Yardbirds: