Soon I'll have some gift cards from Borders and Barnes & Noble arriving. I've never used one of these gift cards so I'm wondering how do they actually work? Let's say I have a $25 gift card. Is the gift card a one time use only in that I can only use it to place one order regardless of how much of the gift card is used? Or can I place an order worth $10, which would leave $15 for use in some other order some other time? Got some decisions to make soon, so I would appreciate if someone that knows could answer me a bit quickly. Thanks.