Eli Greenbaum wrote a terrific article for the Harvard Journal of Law & Technology last fall called 'Open Source Semiconductor Core Licensing'. I'm using the GPL as a place-holder in my verilog source, but I've always felt that the GPL/LGPL were inappropriate licenses for digital logic. Eli's article makes clear arguments on why this is the case.
Here's the link to Eli's article: http://jolt.law.harvard.edu/articles/pdf/v25/25HarvJLTech131.pdf