does your car have abs?
mom had a 96 grand am that went thru 2 sets of brakes in only 16k miles...first time she replaced the brakes and we didn't really think that much about it
then the second set got worse and worse and one morning she came home from work (graveyard) and mentioned that the pedal was going to the floor ....of course i didn't believe her and took the car for a drive...and nearly doo-doo'd on myself..almost no brakes at all
car was towed to the ponti-yuck dealer and was diagnosed as having a failed abs computer and contamination in the brakes lines...cost her 1400 smackers and just one month after the warranty expired and there was nothing the service guy could do to get gm to cover the repairs
someone else also mentioned that getting stainless steel brakelines helped with a spongy pedal