Loss of signal with USB is not all that uncommon. Even USB printers and scanners have to be re-hot plugged occasionally to renew the connection. That is why a hub is handy so it is easy to pull a plug and slip it back in. Usually it doesn't happen during a data transfer, but when a component goes to "sleep."
Hopefully USB 2 is better . . . but my sense is that eventually USB will be buried by Firewire. I have Firewire on a three systems, and have never lost a connection.