Emerce reports on the fact that Paypal is testing a virtual card number system for use on the web. Essentially the Paypal user gets a one-time credit-card-format number. To be used once within a specific time period. Good thing for the Paypal customer base is that it allows them to also pay at merchants that do accept credit-card but don't accept Paypal. And it helps Paypal to increase user value and draw in more money in the account.
Well, this is at least an interesting effort. I'm personally (and intuitively) not sure if this will fly though.