I don't know if it was common in lots of places but they were very common here...anybody remember the 5-band and 7-band "Boostilizers" that Roadmaster used to sell? Pretty much every parts house (Auto Zone and the like) as well as Wal-Mart, Kmart, etc carried them and seemingly everyone that had any kind of aftermarket tunes had one at least for a little while before learning better.
Shamefully I must admit to being one of those who burned their money on that trash before learning better...
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Edit:
After seeing previous posts that must have been made while I was typing mine apparently I'm not the only one who remembers the above-mentioned units.
And phantom420? Just as an //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif it was Stillwater Designs that produced all the Kicker gear once upon a time. One of my first "decent" bass enclosures was a Kicker Super II (though you may not have a clue what that was) and it was clearly labeled "Kicker Super II: By Stillwater Designs" across the top of it.