I have had this card since 2008, and it has generally been a positive experience. I started out with a $1000 credit line (while I was in school) at 13.24% APR. I then received increases to $3500, then $5000, $13,500, and am currently at $16,000, with same base APR. They occasionally have promotions where they will let you cash advance or balance transfer funds at 0% for 12 months--I used this feature last year when I had to replace my roof; don't know where else I could have gotten an $8000 unsecured loan at 0%.
The 3-2-1 rewards are in points, not true cash back (at least on my card). Each point is less between about 1/2 and 2/3 of a cent depending on what you redeem it on. I recommend Discover or Amex over this card if what you really want is bank for you buck on rewards. But this card is great for just basic credit on good terms.