I charge practically everything to the Amex....last year it was about 25k
Many people I know who have American Express Platinum use it to pay for as many purchases as possible because the rewards are good. Supposedly, it is a really good card for perks if you travel a lot which is interesting because, my experience has been that many places in Europe don't accept Amex, but VISA and Master Card are fine. Read that it is good to use for car rentals though.
IMO, using a credit card for purchases is great if you pay it in full each month. Never pay interest if you don't have to. These days, I never have more than $20 in cash in my wallet because everything I buy, I pay for with a card.