Last Chaos Communication Congress,
Harald Welte of
netfilter fame presented
a number of methods to find out and prove GPL violations in Linux-based firmware images that today can be found in a number of end-user hardware. Today, I found his new page
gpl-violations.org, which currently only houses a few mailing lists related to GPL violations, but which will (IMHO) become an authority for GPL violation reports and how to fight them.