Corsaire has released their white paper [pdf] on hacking magstripe gift cards.

This paper is based on research conducted on a large number of UK gift cards. It has been created to complement the presentation “Stored Value Gift Cards: Magstripes Revisited”, which was delivered at the EUSecWest security conference in London in May 2009. It concentrates on magnetic stripe (magstripe) gift card attack techniques and also provides a series of guidelines and tips for developers and systems architects who are involved in the process of implementing their own gift card technology.