Well paypal is easy. It's easy to sign up. It's easy to use. It's fast. And well... it was just very user friendly. I've spent over $200 on PayPal and so far I've had zero problems. Although I had a friend who got screwed out of $170 on a xbox. But if you buy from the right ppl then you shouldn't have that problem. Also they made it fairly easy for ppl on the internet to sell things. Sort of a alternative to EBay, which I don't trust. Now as to what one thing they did to make them so popular I dunno. I couldv'e been that some major companies started using it, then other companies noticed and had to counter back by also using paypal as a payment method, or it couldv'e as easily of been luck. But I have to say EBay has increased there sales super high I'm sure. So who knows how well they were doing before that.