Look at this -statistical data:

Facebook - 300M+ registered users
More than 50% users logs in and use facebook everyday.

Paypal - 66M+ users.
Less than 10% users active everyday.

Given the following facts, it is speculated that "Pay with Facebook" will soon replace PayPal as the number one online payment processor.

Facebook has already started "Pay with Facebook" to some of their apps like GroupCard, PackRat, Birthday Calendar and their own icon gift shop. People can pay via their "facebook credits" which they can add to their account using a major credit or debit card.

In 2007, Paypal's revenue was 1.8 billion dollars (does not include ebay earnings) while facebook earned 150 million dollars. In 2008, facebook was estimated to have earned 350 million dollars, Paypal at 2 billion dollars. This year, that facebook has risen to unimaginable heights, including the addition of facebook ads, and the new facebook payment system, it will not be far from reality that in the long rung, facebook will replace paypal as the leading payment system - if - they could integrate a buy and sell auction system within their site. :D

I will be including links and more information about how "pay with facebook" kills paypal, but maybe it would be in like 3 years...

For more info, look at the sidebars.