Regarding to the Citibank Dividend Platnum Select:
Yes they are giving out 5% for gas and groceries, but then you have to wait till $100 reward, and if you didn't reach $100 before you cancel your account it will be gone. Assuming a mean of $50 not taken when you cancel your account, your unclaimed reward of $50 over a mean of 4 yrs period is $50/4 = $12.5 in opportunity cost.
So for your transaction amount, if you found anything that give you less than $12.5 difference each year but pay you back every billing cycle, go for that instead of the Dividend card.
My Chase Freedom (former shell) give me 3% on gas and 1% everything else just like Dividend, but they pay out every month. I spend about $100 on groceries and $400 on gas every month (4000 miles per month), so that would be a $400 * 0.02 + $100 * 0.04 = $12 difference per month, equal to $144 differences per year.
I encourage everything to calculate. Dividend here I come. =)