How does a gateway IOU differ from any other IOU on the Ripple network? How does a gateway IOU differ from any other IOU on the Ripple network? Say, if I got a $1000 from a gateway, does that make it a better currency than say, creating a second account and sending myself $1000 through that? Does the Ripple network somehow distinguish between those?
It doesn't differ.

Gateways are just issuers that you somehow have more trust for, so much trust that their IOUs can basically be treated like cash.

This is what happens in the current financial system, when you see $100 on your bank account it doesn't mean that you actually have $100. It just means that you hold your bank IOUs.

From what I understand there is no technical distinction between both types of IOUs.