I learned the crossover turn, as a swimmer, over 20 years ago (for the purposes of Back-to-Back turns), and, as a coach, I have tried to teach it to swimmers every season, with limited success. However, after watching the above race, I believe it has to taught...to every swimmer.
The turn is not as easy to learn as some of the other tumble turns, but it is obviously a technique that, when mastered, is superior to open turns. In an effort to find better ways to teach the crossover, I have stumbled across two great videos. First, on YouTube:
The breakdown of each part of the turn is meticulously outlined. All in all a great video.
The 2nd video is a GoSwim.tv DVD "Teaching Progressions with Steve Haufler". The entire video is filled with amazing progressions for teaching young swimmers skills and turns for all strokes. One of the progressions is for the crossover turn. I recommend the entire DVD; it is a must for all club coaches.
The bottom line is that if we are not teaching our swimmers this turn we are holding them back. Even Michael Phelps has started doing it (I think he was inspired to master it when Ryan Lochte started challenging him). Check out the videos...let me know what you think.