The shams, scams and dead ends of the High Fidelity hobbie/passion/adiction

I am not real current so I may have missed a few. The ones I remember are SQ and any other name for "Quadraphonic", Perfect sound forever, and I will see what my fellow A’goNers can come up with. As a bit of a variation on a theme, I wonder what the most profitable B.S. audio trend/product was?...certianly the 8-track tapes sold well.....and ate themselves rather quickly.   

Sould likely have included the second D in addiction...