Note that many Coinbase/Bitpay/whatever transactions will be off-chain - much like PayPal, you can have an account balance that is just transferred in Coinbase's ledger but doesn't actually appear to be transferred on the block chain.
I thought transactions like that weren't supported by the bitcoin protocol. Are there any resources that explain how this works with the general blockchain?
It doesn't work with the general blockchain. If I have 1btc in my coinbase account and I send it to your coinbase account then it never shows up on the block chain.
I think people hugely overestimate how much volume is happening with this though.
