FWIW, my sister-in-law took stopped in LA bound for South Korea without a Visa and wasn't just kicked home. The US embassy ultimately got things sorted out.
Good thing. I'm from Uruguay too :) and I miss the time we were able to visit the US without a visa.
There's also the time when the Pan-American games teams were stuck because the US implemented the visa just at the time they were leaving.
The fact that we can't even transit is very annoying - Miami used to be a big hub for the Caribbean, and flights to Canada are more convenient through the US (I've got family in Canada, and I took the Air Canada Buenos Aires - Toronto flight even though it's more expensive than going through the US, because of the transit visa).
I've never visited the US for that reason (I stood a few miles from the border in Niagara, but it made no sense to go through all that hassle and expenditure for just a day's visit)
