I think it's definitely possible that the U.S. has a worldwide spy operation tracking all international information transfer. But I really hope people understand what would be necessary to implement something like that before they start ranting about U.S. spy tactics.
First of all, most information people are worried about goes by telephone. Other people have done the math, but you'd need something like a terabyte per second of data capacity to store all the information going between Europe and the U.S. alone. So obviously, you need to be able to filter in real time.
This raises the next question - how can you filter tens of thousands of voices in real time? You can't, not without a small city of supercomputers (and that might be noticed). But it IS possible to filter millions of calls based on their incoming and outgoing numbers - the phone company does it every day.
So now we've figured out that the U.S. has a signalling system that in all probability cost tens of billions of dollars and is about as useful as a police wiretap. Furthermore, it's a kind of wiretap that's completely illegal, which would make it very difficult to share information captured from it with the rest of the government, much less private firms.
So what, exactly, would Echelon be useful for? The NSA could be monitoring all our calls just to send news of business deals to competing U.S. firms, but most of the interesting stuff (industrial designs) is still done the old-fashioned way. The network could be a massive plan to ensure that the U.S. has an advantage in every war, but it's highly unlikely that we'll ever go to war against the countries where covert cable monitoring is most effective (Britain, France, Germany, etc.) What about across the other ocean? Well, if you're trying to monitor the Chinese army, tracking calls made on undersea fiber seems like a massively inefficient way of doing this. After all, you can just send an EP-3 over their airspace and have an army of mathemeticians and linguists figure out what they're saying....
If Echelon exists, it sounds like a terrible waste of money for the American taxpayers. My (unsubstantiated) theory is that the appearance of having an international sigint system is beneficial to the U.S. government, in that it encourages other countries to maintain alliances with us lest they be spied upon by the all-powerful Echelon.
Keep in mind that although I don't think the existence of Echelon is likely, I'm fully prepared to eat my words in 20 years when their's a big expose and it becomes obvious that the U.S. was spying on everyone else. In the meantime, I do encrypt all my e-mail...just in case....