Picked up this book by Jessica Livingstone (Co-Founder of YC and wife of Paul Graham) - I like the style of the book as its interview Q&A based hence unfiltered. But its like really really old. It was published in 2001, even Twitter only started a few years later.

1. First chapter is on Pay Pal (refer to the attached) - I thought it was kinda odd how they did not mention who the CEO of x.com was throughout the conversation (but he said they made amends and are friends now)

2. This other part was informative :

Livingston: Was the growth viral?

Levchin: We built the system to be viral from day one. The idea was: I can send you the money, even if you aren't a member. If I send you $10, you get an email saying, "You have $10 waiting for you. Sign up, and you can take it." That's the most powerful viral driver there is. Free money available to you.

For eBay buyers and sellers, it became this crazy loop where buyers would be like, "I want to pay you with PayPal," and sellers would be like, "I don't accept PayPal." And buyers would say, "That's OK. I'll just send you $10, and you can sign up." So the seller would get infected, and the seller would say, "Oh, this is really simple, so I only accept PayPal."