Since I've got the Amex Platinum on my mind right now, I'll share one other piece of information. According to Amex, the Platinum card will soon lose one of its benefits. For some time now, Amex has given Platinum cardholders a 20% rebate when they used Membership Rewards points to pay for travel through the "pay with points" feature. Well, as of February 1, 2013, that benefit is going away.
I'm not too worried about it, since I've never used the "pay with points" feature myself. For those who do use it, though, that's a significant benefit reduction.