Apple was recently granted a patent for a camera system that would allow users to snap a picture and then adjust the focus after it was snapped. We've already seen this technology from a firm called Lytro (see sample above), so we presume Apple's system works differently on some level, and Nokia's Refocus app uses software to allow similar tweaks on some photos.
Apple's patent describes a "digital camera system configurable to operate in a low-resolution refocus mode and a high-resolution non-refocusable mode comprising: a camera body; an image sensor mounted in the camera body having a plurality of sensor pixels for capturing a digital image; an imaging lens for forming an image of a scene onto an image plane, the imaging lens having an aperture; and an adapter that can be inserted between the imaging lens and the image sensor to provide the low-resolution refocusable mode and can be removed to provide the high-resolution non-refocusable mode…" Clearly, this is a hardware based system instead of software-based, like Nokia's option. However, it could allow you to snap a quick picture without needing to wait for a focus, and then let you set the focus, clearing your subject up, after you've already snapped it.
Lytro hasn't been particularly popular, likely due to its awkward design, and Nokia's solution forces you to launch a separate app to snap the photo, which takes longer than simply launching the camera. Apple's solution could put the technology in more hands, particularly if it's ever implemented into an iPhone, though for now it's simply just a patent.