Google Checkout and Paypal simplify online payment for both the customer and the business.  The customer creates a Google Checkout (or Paypal) account once, and register one or more credit cards, shipping address, and billing address.  When they want to buy something from a merchant that accepts those services, all they have to do is press the appropriate link and enter their userid and password for Checkout or Paypal.  That's it.  The customer doesn't have to create a separate account for each merchant, and the credit card number stays protected. 

Google also preserves the customer's privacy so the merchant doesn't know their e-mail address.  On the flip side, the merchant doesn't have to register with multiple credit card companies but only with Paypal or Google Checkout.  I see many companies now accept Google Checkout (including some big names like Ritz Camera which takes both GC and Paypal).  Plus a charge of 2% of the transaction is a lot less than what some banks charge via the old credit card machine thing.