For ten years, I've been building up a bunch of standard advice on GPL compliance. Usually, I've found myself repeating this advice on the phone, again and again, to another new GPL violator who screwed it all up, just like the last one did. In the hopes that we will not have to keep giving this advice one-at-a-time to each violator, my colleagues and I have finally gotten an opportunity to write out in detail our best advice on the subject.
Somewhere around 2004 or so, I thought that all of the GPL enforcement was going to get easier. After Peter Brown, Eben Moglen, David Turner and I had formalized FSF's GPL Compliance Lab, and Dan Ravicher and I had taught a few CLE classes to lawyers in the field, we believed that the world was getting a clue about GPL compliance. Many people did, of course, and we constantly welcome new groups of well-educated people in the commercial space who comply with the GPL correctly and who interact positively with our community.
However, the interest in FLOSS keeps growing, rapidly. So, for every new citizen who does the research ahead of time and learns the rules, there are dozens who don't. The education effort is therefore forever ongoing because the newbies always seem to outnumber the old hands. It's our own copyleft version of Eternal September. The whole space is now big enough that one-by-one education in our traditional way can no longer scale.
Hopefully, publishing some guidelines for GPL compliance will help the education effort scale. If you redistribute GPL'd software commercially in any way, or you are a lawyer who represents people that do, please spend the time to familiarize yourself with this information. If you have ideas on how we can expand this document, we would of course love to hear from you.
Update (on 2008-08-26): Thanks for all the feedback we've gotten from the community. We've been glad to update the document to incorporate your suggestions.