TomTom Go TomTom (check out the cool TomTom Go) one of the leading GPS navigation software and systems manufacturer was forced by gpl-violations.org to publish their Linux kernel source under GPL.

The source code for the Linux Operating System Kernel, including TomTom's own modifications, is now made available at http://www.tomtom.com/gpl.
As part of the agreement, TomTom will show it's appreciation of the Free Software and technology enthusiast movement by making a significant donation to the Chaos Computer Club.
Even if its free, there are still rules to comply with, like giving back. This is an important lesson for Software vendors, they need to check their source code to make sure they comply with the GNU GPL License, they might end up having to release propriatary technology, which can become a big problem.

The gpl-violations.org project is a volunteer-based effort to make corporate distributors of GPL-licensed Free Software aware of the licensing issues involved with GPL-licensed software.
More details on GPL-violations.org.