<wonder-ment at loss of brakes after donwhill run snipped>

it be called 'brake fade'

the pad's coefficient of friction goes to nil with a dramatic 
resultant loss of braking ability.  the stink is you.  i mean your 
brake pads getting the binding resins cooked to bejeezers.

and lastly, the pedal sponginess was possibly getting the calipers so 
hot that the brake fluid boiled in the caliper-- gives a feeling like 
air in the line but goes away when everything cools downs.  water 
contamination can lower the boiling point of brake fluid.

'riding' the pedal isn't necessary to get the brakes this hot.  
frequent applications without a cool-down period accomplishes the 
same thing.

solution?  install a Jake Brake (ask Joel)  :)

-dan