Dpreview has posted up a video that shows a comparison between CDAF and PDAF the two mainstream types of auto focusing in photography industry. Video shows CDAF (Contrast Detection auto focusing) works faster when compared to PDAF (Phase Detection Auto Focus) when taking photos of still objects.
Differences between both systems is that while CDAF focusing measures contrast of color tones reaching sensor through lens. Though this focusing system is more accurate to still objects it suffers when tracking objects or taking photos of fast moving subjects. PDAF focusing method splits light into pairs and compares both. It is rather slow when taking photos of still objects but works well for fast moving subjects.
There are now cameras using hybrid CDAF and PDAF focusing systems as the Nikon 1 J1 and the Nikon 1 J2 are an example. Though still not perfect this may prove to be the best solution as will work well for both stills and fast moving objects.