Of course. If you don't, you can't use the code. Thousands of companies and millions of individuals are abiding by these open source licenses every day.

I can't imagine actually picking through one of them and making strategy decisions based on them.

Then you can't use the code. You'll have to buy non-Open licensed code, or write it yourself.

Has anybody ever actually been called on it?

Yes. Though it rarely comes to lawsuits. The GPL is a pretty strong license, from a legal perspective. The people who've tested it aggressively have suffered the consequences (SCOX, for example). Some others (The Artistic License, for example) are more questionable and less strong from a legal perspective, but even the weak ones have proven to hold up pretty well in court (there is an ongoing trial involving the Artistic License, though sort of indirectly, but it seems to be holding its own in the eyes of the law).

Are there really companies that have open-sourced their entire product just because they use some random little GPL library?

You've already admitted to being willfully and proudly ignorant about Open Source licensing in multiple posts in this thread. So, why are you being so damned pushy about sharing your ill-informed opinions on the subject?

You are assuming the GPL is intended as a trap to lure unsuspecting businesses into being forced to open their code. It is not, and it's a symptom of your ignorance that you think it is. It is a license that allows anyone to use the code, provided they share the results under the same terms. In the event of a license violation (which is in no ones best interest), there are many possible outcomes, only one of which is opening of everything the code ever touched. Law, including copyright law upon which the GPL (and all other software licenses) are based, has many shades of nuance.

I tend to avoid using 3rd party code, as it invariably ends up being garbage

This says more about the limits of your experience than about Open Source software or licenses, and is not relevant to this discussion.

I think of places I've worked in the past and the people who worked there. Would your typical VB developer in a typical corporation know about this stuff? If he did a google search for a code snippet to perform a task, and ended up on SourceForge, would he read the license or would he simply drop the code into his project and get on with his day?

I think hanging out on sites like HackerNews, filled with some of the smartest programmers around, clouds our perception of the "typical programmer". I've worked at a lot of shops over the years, and I can count on one hand the number of devs who I might ever expect to find here.

Possibly not (I have been involved in Open Source in the context of a business for over ten years now, so my experience is perhaps longer/deeper than some, particularly in the areas where business and Open Source bump into one another), but I rarely meet a developer that doesn't at least know the basic differences between the GPL and a "BSD-like" license. Knowing those two is actually most of what you need to know to develop with Open Source software without handing the legal stuff over to luck.

But, saying "the typical developer doesn't understand" software licenses is no excuse for not abiding by the terms of the license. That is the price you pay for admission to a wide world of awesome software that is enthusiastically free. You either pay the price and learn what the licenses of the software you want to use mean, or you simply can't use the licensed code. It's both an ethical issue and a legal one. I can't force anyone to hold to any particular ethical standards, but, the copyright holder can certainly make your life difficult if you don't follow the legal requirements.

I think folks who don't take licenses seriously don't understand how strong copyright law in the United States (and most of the developed world) really is. If someone comes after you with a provable claim of infringement, it could cost you a lot of money. I've been involved in a copyright suit, and the results were that the infringer ended up settling for $30k, even though no money was being made on the copyrighted work (I was giving it away for free, and so there were no losses on my part; but copyright law allows for multiple layers of penalties and had it gone to trial it would have cost them at least that much).

If he did a google search for a code snippet to perform a task, and ended up on SourceForge, would he read the license or would he simply drop the code into his project and get on with his day?

Sure, people violate copyright all the time. People also pirate software all the time. It doesn't make it OK, and sometimes folks get caught doing it and it costs them or their employer a lot of money, time, or both.

I think hanging out on sites like HackerNews, filled with some of the smartest programmers around, clouds our perception of the "typical programmer".

Open Source programmers tend to be towards the smarter, and more importantly better informed, end of the scale. That doesn't account for the problem you mention of proprietary programmers "borrowing" liberally from Open Source projects without abiding by the license. But, when those things happen and they are exposed, there's usually a shitstorm over on Slashdot and the company in question gets harangued and ranted about and blogged about and occasionally sued until they comply with the license (either by rewriting the offending code and making a monetary contribution to the FSF of EFF, by way of apology, or by giving back their changes and using the software according to the license). One such case was discussed here on HN just a couple of weeks ago.

It happens all the time, and only a small percentage of people who use Open Source software without abiding by the license are ever caught. But, I'd like to think that things are getting better as awareness of Open Source increases.

I needed a wrapper for the Native WLAN API in Windows XP/Vista, and hey, there's an open source (LGPL) library available. I ran the license by our lawyer (we actually produce packaged software), and while the LGPL would have allowed us to use the library in closed source software, he thought the inclusion of the LGPL license regarding a library could have potentially scared our users (who need to maintain the integrity--and secrecy) of the data our software is used to collect.

This wasn't ideal from my perspective, because now I had to write the wrapper knowing that the code existed and I could just sit there and copy it. But I didn't. And I probably know more about the Native WLAN API because of it.

Anybody know of a case more along the lines of '[random PHP image rotation library from SourceForge] vs. rtatr.com (rotate your images online!)'?

http://www.gnu.org/copyleft/gpl.html

To “propagate” a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.

To “convey” a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying.

The GPL (v3, at least) restricts conveying.

GPL v2 states the following:

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

So long as you do not distribute your modified copy, there is no need to abide by the conditions following that section.

Huh? So what do you do, re-implement the whole world from assembler up?

Think Open Source CMSs and Javascript libraries. Anybody who's been burned by enough of that sort of thing quickly learns to avoid it. 3rd party Javascript is especially bad in this respect, generally requiring a complete rewrite before it performs the task it was advertised to perform.

Can't argue that most JS examples you'll find on the web are awful, though, or that open source CMSs are typically useless. Or closed source CMSs for that matter.