I have consciously released the majority of the software I developed under a copyleft-style license, i.e. a software license that ensures that its inherent freedoms are passed on to downstream recipients, including any modifications that a third party may have.
Around 2003 it became apparent to me for the first time that several companies were blatantly ignoring their obligations under the GNU General Public License (Version 2) for the netfilter/iptables software.
I took it on to enforce the license on those who are in violation and managed to get the license successfully enforced in hundreds of cases that followed. Most could be resolved out of court, but some had to actually go in front fo a court.
The license enforcement related work became so comprehensive, that I started a separate project to deal with this, the gpl-violations.org project. More about the activities there can be found on the project home page.
As of 2011, I was too busy to push forward more enforcement related work, which is a pity. I still hope that at some point I can pick up again and conntinue. There certainly is no lack of companies being ignorant about their obligations.