Personal data.
Those are the 2 words uppermost in my mind when using credit/charge cards. I will not purchase on the internet unless I can establish a line of credit via another method, eg. phone, mail, bank to bank and for a single transaction only.
When making purchases using those cards I alway ask for and get the carbon which was between the 2 documents when swiped ( Ever seen a garbage bin full of carbons? frightening ) the garbage remains outside the stores for up to 7 days.