In continuous focus mode the image in the viewfinder will hunt back and forth, and never really appear to lock on. Howver this doesn't mean it isn't working....
Best settings I've found are to:
a) Make sure High Performance mode is on (under power settings somewhere)
b) For continuous focusing use one of the central 9 set of AF points
c) Set the release mode to 'focus priority'. This ensures the camera only takes a picture when the image is in focus.
d) Use either CH or CL
e) In the lower-left of the view finder you should see a green circle appear when the camera has found focus (even if the view finder still appears to be hunting.
Sorry if the above isn't absolutely precise - don't have my camera with me at the moment.
With these settings, even though the viewfinder appears to show the camera hunting, I've had really good results in continuous focus mode. I don't shoot BIFs, but for situations where I have tried it (kids running, vehicles, animals and birds on the water/ground) I've got really good results.
Hope that helps,