Can you use a barnes and noble gift card at Amazon.com?

No. There have been reports that Barnes and Noble purchased Borders. This is only partially correct: Barnes & Noble aquired the Borders nmae and trademarks, They did not purchase or take on any of Borders debt, which is what the gift cards were. If you failed to redeem the gift cards while Borders was liquidating, the debt was lost and the cards no longer have any value.