I just watched the Phelps 200 meter world record race and his turns were lethal

Michael Phelps' world record for the 200 was greatly assisted by his turns. He was easily getting 10 meters underwater before emerging to the surface with absolutely no loss of momentum whatsoever. His turns were so devastating to his competitors that Van den Hoogenband; (silver Medal), would take up to two-and-a-half strokes before Phelps' took his first.

To a master swimmer who competes or even a triathlete who duck dives when entering or exiting to or from an open water event, this accomplishment stresses the importance of doing butterfly regularly.

Herald Sun: [Link]
Sports Australia: [Link]
The Guardian Limited: [Link]
Chicago Tribune: [Link]
This is London: [Link]