If you want to do things manually, you can try NirSoft's
USBDeView. Until I find something better, that's the route I've gone.
I use LANSweeper to generate a list of systems and a batch command for each machine, copy/paste the list of commands into a .bat file (actually several .bat files that I run simultaneously in order to speed the process up), then copy/paste the output into a little Access database in order to filter the results. It's a kludge, it takes a little time to do, but those who wanted to see the USB activity have been appreciative.