Last year Walmart got into some trouble for claiming it saved shoppers $700 a year just by shopping its stores. Competitors took issue with the claim, as did the National Advertising Division of the Council of Better Business Bureaus, and the ads were pulled. But Walmart is at it again, saying it can save shoppers $28 a week with its latest round of reduced prices. That's more than twice the amount it claimed that got it into hot water last year. Is it true?