Zonker over at NewsForge talks about the challenges that are being faced while enforcing the GPL. He talks about how violations are found and handled, & what we can expect with the coming GPLv3.

"Violations of free software licenses are usually handled differently than violations of proprietary software licenses. Developers aren't looking for money or to punish competitors, but simply to enforce compliance with a license that requires reciprocity. Though a few violations have been widely reported, many more are settled quietly."