PayPal already has a partnership with MasterCard in place that lets you use its debit cards in stores, but the company has now expanded that retail presence even further with a new deal it's struck with Discover. Starting sometime next year, that arrangement will let PayPal customers use their charge cards at any of the 7 million retail locations that accept Discover cards, with funds drawn directly from their PayPal account. What's more, PayPal says that retailers won't have to make any hardware or software upgrades to accept the PayPal payments, noting that they'll simply have to let customers know of the new option with in-store signage. Of course, the deal also likely has implications beyond traditional plastic cards, as P
