I'm hoping that one of the other engineering types may have run across a solution here.

I am looking for a device that will allow me to monitor the connection between a USB host and a USB slave. The host is a headless embedded processor, so this needs to be a physical piece of hardware that I can insert between the two.

I don't know enough about USB to be certain that I'm speaking in the proper terminology, but essentially I need to be able to analyze packets flowing in both directions, as well as any relevant state information. Think of an ethernet packet sniffer, but for USB.

Googling has produced a number of results, but there's nothing like first-hand experiance.