Just a warning: the primary reason for using PayPal over directly taking credit cards is that the latter subjects you to significant, onerous legal requirements for maintaining the security and privacy of your customer data.
Unless you have the money to spend on compliance, Paypal/Google Checkout/Amazon Payments is the way to go.
This doesn't quite answer your question, but it is a reason for not taking credit cards directly.
I completely agree - PCI/DSS pretty much means that your network is designed by lawyers and auditors instead of network engineers/sysadmins. It's a very unpleasant state of affairs.
It certainly can't be said that all of the payment card industry's requirements definitely increase security.
Unless you have the money to spend on compliance, Paypal/Google Checkout/Amazon Payments is the way to go.
This doesn't quite answer your question, but it is a reason for not taking credit cards directly.