TandemGeek

True. The reductions associated with reduced rotational mass are just about negligible. Reductions in aerodynamic drag always trump rotating mass which is why professional cyclists routinely trade-off reductions in aero drag for increased wheel weight associated with very deep section rims. There's actually some pretty good information that's easy enough for just about every average Joe to understand here on the subject: http://www.biketechreview.com/archive/wheel_theory.htm

I'm not sure how many different types of wheels you've used on the same bicycle or tandem, but based on my own experience over the years different wheels, tires and changes in tires and tire pressure as well as different types of road surfaces will all produce changes in sound and road feel that produce the perceptions you mention. I tend to caveat most of my observations in this regard with the words "feel _____" because, frankly, the sensation you get from a conventionally spoked 36h wheel are different from a Rolf Prima Vigor and a Topolino AX3.0T.

Case in point, a lot of folks who have been riding a stock 40h tandem wheelset with wire-beaded 28mm tires that tips the scales at nearly 3,600 grams once you add in the tubes and rim strip tape can truly feel the difference when they drop nearly 2lbs by moving over to lightweight racing wheels with narrow, higher pressure tires and that's what we often hear in terms of feedback. Add in the the reduction in wind noise that comes from removing 1/2 the spokes from the front wheels coupled with bladed spokes and a deep-section V-rim + the more lively feel that the less compliant tires and wheel provide and even a 350lb tandem will feel much more lively and spry, even if the actual performance change is on the order of 1% - 2%. Then, add to that the placebo effect that comes with any 'performance upgrade' and there you go.