Perhaps the most important technological advances to help improve swimming technique is the use of underwater video analysis. Recently Olympic medalist Gary Hall Sr, coach of The Race Club and a USMS member, has posted a detailed analysis of the underwater freestyle pull. (If you have trouble viewing the videos, you should try the Race Club Youtube channel.)
The Swim Smooth Blog has also posted an excellent analysis of the underwater freestyle of the male and female 2011 World Champions in the 1500m freestyle: China’s Sun Yang and Denmark’s Lotte Friis. Their techniques — from Yang’s emphasis on distance per stroke to Friis’ high turnover and straight-arm recover — make for an interesting contrast.