Terry has a series of blog posts with very thorough and judicious discussions of all the different toys, or "tools"; the one on paddles is dated December 26, 2010 (http://www.swimwellblog.com/archives/945
.) "Hand Paddles are a clear and present danger to shoulders and encourage misguided focus on power. If you use them at all, swim ó donít pull ó at moderate pressure with a meticulous stroke." I don't have data, but my observation is that most people who use them a lot get shoulder injuries eventually, since they almost inevitably overload the rotator cuffs. Plus, they don't make sense in terms of improving your stroke -- quite the opposite, really, as Terry explains in that post. The whole series, on fins et al., is great.