> I bought a house for cash in Las Vegas after the crash and the bank never once asked where I got the funds to do so. I'm pretty sure they were supposed to.

Umm, no. It only. I, but that's frightening. You have a right to privacy in a private transaction like that. Where you will run in to a ton of questions is when you use a big chunk of money for a down payment on a mortgage. In that case the bank wants to make sure you didn't borrow the down payment and get in over your head.

The US has no general right to privacy, and all large transactions are potentially notifiable to the anti-money-laundering authorities. This is what HSBC got in a lot of trouble for not doing.

Any notification would go as far as that - simple notification of a transaction. There's no requirement for the bank to investigate the source of your funds as part of a private transaction.