Being a new PP Classifieds user, I recently noticed that only a single payment option can be set for ad placement: PayPal, or Authorize.net, or WorldPay, or etc.
Some will want to use PayPal and those who don't have PayPal accounts will want to use their credit card. Since Classifieds doesn't have a multiple payments option, it's impossible to make all the customers happy. The PayPal users will have to use a credit card or the credit card users will have to sign up for a PayPal account they may not want, depending on which payment method a Classifieds admin decides to go with.
PayPal's Website Payments Pro is an integrated payment gateway solution that processes credit card payments without the customer ever knowing PayPal is the payment gateway. And of course, the customer is given the option to pay with their PayPal account if they don't want to use a credit card. The nice thing about it is a customer who is paying with a credit card doesn't have to sign up for a PayPal account and is never redirected to PayPal's website to collect their payment.
If PayPal's Website Payments Pro is not in the PhotoPost pipeline, maybe you'll consider it in the future?