I've recently started scratching out the credit card number and the expiration date on paper receipt copies given at the time of sale (leaving the last 4 digits visible). The last four + transaction code and date are all the vendor needs to account for the sale. This (so I'm told) is a good thing for everyone to do to prevent your credit card number and exp. date from being horked. I've only had one ass hat complain about it and as a result he lost the sale.
Everyone else has apparently collected their money just fine. I've certainly been billed correctly so apparently everyone is happy and I'm not leaving my VISA number every damn where.