I googled it for you
http://www.borders.com/online/store/PopupView?storeId=13551&catalogId=10001&langId=-1&page=popuptermsconditions4. REWARDS REDEMPTION.
Borders Bucks are redeemable at Participating Stores and cannot be combined with Discount Programs (except the Classroom Discount program). Borders Bucks cannot be used towards the purchase of any of the following items: Borders Rewards Plus membership fees, certain eBooks (see applicable eBook product detail page at the time of purchase to determine eligibility), gift cards and certificates, rush fees, special-order deposits, shipping charges, gift wrap charges and tickets. Borders Bucks have no cash value and are not applicable to prior purchases. Borders Bucks that are not redeemed (or, if eligible for donation, donated to an eligible teacher) by the end of the month earned will be forfeited.
In lieu of redemption, eligible Borders Bucks may be donated to teachers enrolled in Borders Rewards or Borders Rewards Plus and the Classroom Discount program, who sign up to receive such donations. Only Borders Bucks which have been earned by making the requisite amount of Qualifying Purchases, as applicable, are eligible for donation; notwithstanding anything to the contrary in the foregoing, "Bonus" Borders Bucks, Borders Bucks acquired via special promotion or accommodation, donated Borders Bucks, Borders Bucks acquired by means not requiring Qualifying Purchases, and any other Borders Bucks determined by Borders from time to time in its sole discretion, are not eligible for donation. Donated Borders Bucks are subject to the terms and conditions of the Program and the Classroom Discount program. Donated Borders Bucks not redeemed by the end of the month following donation will be forfeited.