didnt know about the grace period. and ur right some places dont take amex. i do have a visa and a mastercard as well that are better than my bmw card at 14 and 16 %. i only pay 60 a year for my amex, well worth it if you consider all the free shit i get from them.
ADD: if i remember correctly the dealership gave me an incentive to sign up with the card. i dont remember what it was tho :/