In the wake of Borders recent announcement it's folding up shop, those holding gift cards from the bookstore chain may have cause for concern. While the second-largest bookseller says it's presently honoring gift cards, shoppers are well advised to use up their balances before it's too late. We faced a similar situation when Blockbuster and Circuit City filed for bankruptcy and are likely to do so again. To ensure consumers don't get left in the lurch, here are a five lessons we've learned from these experiences.