Cristian, on a single bird the cameras do a fair job on C-AF, but if your trying to track fast cars or a group of bikers or multiple objects coming your way the cameras keeper rate is very low,, shooting from the side or at a 45 degree angle of movement is a lot different than head on with some speed,,
my last film camera was a Nikon F5 and it would continuously track about anything I ever wanted it too handle, not so with my E3,, I do not even try C-AF anymore as it has failed me so many times,, just stick with the S-AF and feather the release and it does fine,,
Derry