Book membership pays off?

After hearing this morning how many gazillions of people are signed up for the Borders Books card - 20 million accounting for one in five households - I decided it was time to figure out if this card, and a similar one at rival Barnes & Noble, make sense. Here's the breakdown:

Borders VS. Barnes & Noble
Cost: Free VS. $25
Applies online: No VS. Yes
Perks: $5 for every $150 you spend plus coupons every Thursday VS. 40% off hardback bestsellers, 20% off adult hardcovers, 10% off paperbacks, CDs, kids books, cafe purchases
Makes sense: Yes, if you don't mind giving out personal info VS. Not unless you buy a LOT of stuff at B&N. Best case scenario - everything you buy is 40% off - you need to spend $63. Worst case - everything is only 10% off - you need to spend $250. So if B&N is your daily source of Joe, go for it.

Thanks to my sweetie for checking the math. My earlier post that you only needed to spend $33 was, sad to say, wrong. Babe, do you get tired of always being right?

Caveat: have to sign up in person for the Borders card.