Optional Under-the-seat Sub-Woofer

I purchased my '04 WRX about a month and a half ago and have been debating whether or not to drop the cash on the optional sub-woofer that fits under the seat.
Just curious if anyone here has that option and is it really worth spending the cash on? Granted it won't be anywhere near as much bass as droping a box in the trunk of the car, but I don't want to give up the trunk space this time.
Any opintions would be appreciated. Thanks.

its gona cost more than a small enclosure somewhere else...the factory charges and arm and a leg for what you get....i personally thing even putting a small 8 in woofer in the corner of your trunk you would be w whole lot happier, and it will cost less....but thats just my opinion

That's the thing. I don't want the dealer to give me any hassles about voiding any electrical warrenty if I do it myself as I have always installed my own systems. I had a Talon previously and didn't install my subs until after the warrenty expired.
I would prefer though not having to run wiring the length of the car again as I'm getting lazy in my old age. The front seat just seems so much easier and space saving.
I'd rather just drop the $250 the dealership is going to charge, but I would like to know if their sub puts out enough 'thump' to make it worth my money.

if its "thump" your looking for then no...basically it gives it enough bass to sound good, but its not gonna give you that boom boom boom you hear coming down the road, its a mild bass note fill in the lack there of in stock speakers