yup tom. thats why i tune amplifiers the same as etl explained.
i turn everything all the way down on each amp, turn all the settings up on the deck (EQ's, volume, etc) then turn the amp up until the speakers distort, then turn it back....
that way, even if the gomer who own the car turns their bass all the way up on the EQ on the deck and crank the volume, it doesnt damage the speakers.

in fact, we have stickers at our best buy store that we would put over the knobs on the amp, so that if someone tries to screw with it themselves, their warranties on everything is void.

also, regarding overpowering speakers. New spakers have filters on them that they only take the amount of current that they need to operate at full capacity. so its virtually impossible to overpower speakers nowadays.