Cash back credit cards

I have always been pretty wary of credit cards in general, but I opened a new bank account last year and found that they had a cash back credit card. The one I have gives me 1% back on all purchases, 2% back on grocery purchases, and 3% back on gas. For me, this has been a great way for me to improve my credit rating (I have it set up to auto-pay the full balance each month) and save just a little bit on the essentials. I think it is one of the better ways to use a credit card, what do you guys think?

 

My sister has either the same or very similar credit card that you do. She makes all of her grocery and gas purchases with this card and literally comes home and sets aside the money for the groceries to ensure that she has the funds to pay it off every single month. She ends up earning about $30 a month back, but she has pretty high fuel costs from her lengthy commute and her grocery bill is high as well with her picking eating and large family.