Guys, no one person is getting $3B on this.
There are the founders, the early-stage VCs, the later stage VCs, the employees...
In order to get funding they had to give up bits and pieces of their company along the way.
Typically these offers would require the owners to stay working at facebook for ~4 years after the deal.
To put it in normal person terms: Let's say you owned a house you built that is worth $500k. You put some money down and have paid off some of the mortgage you used to buy the land/materials/etc, so let's say you've got $100k of value in (some consisting of cash you put in, and some consisting of labour when you built the house) and a $400k mortgage. Now some property management company comes off the street and offers you $450k for the house.
People in this thread are all: holy shit! $450k is a ton of money. I'd take it and go blow it on yachts and booze and blow and hookers!
But you don't get all the money. You have to pay out the other owner (the bank). You also aren't getting the full value ($500k). Also, the property management firm requires you to work for them as a super for 4 years. You have to do all the repairs and maintenance etc, and it's a full-time job. They'll pay you for it, but you gotta do it as part of the deal.
Would you do it, or would you wait to see if someone would pay you $525k?