Little math problem for you:
I have a 20% off the list price of any one item at Borders. The coupon cannot be used online and must be redeemed by no later than 2/3/2008. The Doctor Who Season 3 DVD has a price tag of $99.00, which means I would pay about $83 (don't forget the sales tax) for it if I use the coupon.
Not bad, right? Until you you go to http://www.borders.com and see the exact same DVD for $69. No coupon, no sales tax (thanks to their partnership with Amazon), and free shipping = $69.
$69 < $83. You could take the money you saved, go to Borders, buy a magazine (~$10) AND a fancy coffee drink (~$4), and . . . ponder what are you gonna do with that coupon?