MITBBS 上的giftcard版上经常有些link,下面这个市最近的。

发信人: amolin (亢猪有悔), 信区: GiftCard
标  题: TE+ link
发信站: BBS 未名空间站 (Fri Sep  8 13:25:04 2006)

https://www.membershipme.com/Offers/Pages/OfferPages/YFD/EPA/KMT/510/index.
aspx?ID=98958AA347B3BB5B20CC1585BB5B38E6&siteid=2ac31210bf&refid=
ym10414574354167711x
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※ 来源:·BBS 未名空间站 http://mitbbs.com·[FROM: 144.212.]

depends on if you buy other cards or not, there are also amazon.com and target cards in this program, and some restaurants.  If you only use shell, there is 125 limit for monthly purchase, so the max rebate for shell card is only 25,  you only save 5 bucks.  I do not think it worth it.  You can also buy shell card on the second hand market at Mitbbs for 10% off. 

If you get other cards, then it may worth it.

or you can try to use the method in the MITBBS giftcard board to try to get the annual billing option within the trial period, then it is only 30/year.  With this it will be much better option.