I regularly read FatWallet Finance Forum. Today, there is a discussion surrounding buying gift cards thru grocery stores and taking advantage of Citi's 5% cashback offer for grocery store purchases (as in the Dividend Platinum Select® Card).
I am usually a naysayer of gift cards - I see no use of giving cash to companies for free for future purchases, not to mention potential issues like maintenance charges and expiration periods, but if the strategy can easily earn 5% back, it is definitely worth some trying if you already want to make a big-ticket purchase from Circuit City, Best Buy and alike pretty soon. (The drawback may be: if for some reasons you need to return the purchase, you will end up with a large cash balance in the gift cards.)
On a similar occasion, the 5% Citi rebate changes dynamics in gas filling too. I used to fill gas from Arco a lot because it can always offer a price 5 cents or more lower than the other chains. However, Arco only accepts check card (and will assess 35 cents transaction fee). With gas prices above two dollars a gallon now, I am using Safeway and Chevron now: the 5% cashback is worth more than 10 cents per gallon, effectively eroding Arco's price advantage.