I am already grabbing USB packets in my windows VM (MfgTool and sb_loader are windows apps), and I have software to replay them (as USB macros). I used wireshark a lot when it was still Ethereal. I actually paid big $ for a commercial ethernet packet sniffer back in the 90's. It came on a floppy disk... wireshark is "more better".
In my linux proggies, I just use printf() to display the USB traffic that I am interested in. Thanks for the tip. It will be easier than writing built-in debugging instrumentation.