Thanks, that is interesting. We tried to put in USB to one of our products at work (a motor drive for a vacuum pump), and it failed as soon as the motor started! With improved filtering we can get past that, but we still have trouble with EMC tests. The problem is that the USB falls over, and doesn't recover, which for industrial control is not acceptable.

I think in low noise/office type environments USB is fine, when you get too near heavy kit it is just not up to the job. People's experience seems to match what we have found.

Ethernet does seem like a much better alternative, it's cheap, robust and widely supported.