Thanks. I had not heard of Alex Webb, but now I'll have to check him out.
The technique that I learned from the birds-in-flight shooters is to prefocus on a particular area, and then vary the focus a bit forwards and backwards while the camera is shooting continuously on its slow burst rate. You don't want a fast burst rate (like 10 FPS on the Sony NEX) because you get too many duplicates for not much focus change. It was easier for me because I knew the skaters were coming at me and where they were jumping, so I could not only prefocus, but also just vary the focus mostly in the direction that they were coming at me. Also, since I shoot RAW only, I turned on the B&W filter mode with its sharpness and contrast turned up all the way up so I could more easily see the red focus peaking edges. I think I averaged about 1 good shot for every 4.