The revision of The Tau Manifesto that launched today includes a wealth of new material, including a rebuttal of the "Pi Manifesto" (http://tauday.com/tau-manifesto#sec:the_pi_manifesto_a_rebut...) and a new section on the volume of a hypersphere:

http://tauday.com/tau-manifesto#sec:volume_of_a_hypersphere

If you thought the original quadratic-form argument for circular area was good, prepare to be blown away by n-dimensional spherical volumes.