One negative aspect I discovered myself some days ago too, shooting some birds in flight:http://www.dpreview.com/reviews/canon-eos-70d/12:
"Sadly Dual Pixel AF is only really used for single image AF or movie shooting (see the movie page to see how it does). If you need continuous autofocus with tracking, you have to use the 70D's conventional AF system. We looked at how well it could track a subject walking towards the camera and left-to-right across the frame."
It is a pity. It would be a great advantage to use the new AF in tracking moving objects.