Facebook as a Bank?
http://michaeldeshazer.wordpress.com/2011/02/27/the-yuri-milner-connect-how-facebook-will-become-a-bank/
This is a little bit of a leading argument but it seems to sum up external arguments.
I still have yet to rediscover where I saw that Facebook was filing to be a bank.
http://en.wikipedia.org/wiki/Fractional-reserve_banking
$2billion in cash can lend out $18billion in value.
@ 5% interest that's $900 million a year in profit.
@ 10% that's $1.8billion a year.
& that's just on interest.
Facebook makes transactional profits too, so on $18billion in credits, I bet you could see $100 billion in transactions if they one day allowed peer to peer.
http://en.wikipedia.org/wiki/Financial_transaction_tax
Visa has about $2-3billion a quarter in revenue via their transaction fees.