I'm not a huge fan of the GPL. While I agree with the FSF on most things, I can't help feeling that the GPL shows a certain lack of faith in the whole idea - if the open source development model is so much more efficient, and Free Software is so much more valuable, then why do they need such a mass of legalese to protect them?
From a more pragmatic standpoint, the GPL is about the most incompatible Free Software license around. If you write GPL code, you can't use it in a BSD, Apache, X11, MIT, or Mozilla licensed project.
I was fairly happy with the LGPL until recently, however. It is a bit more restrictive than I'd have liked, but as long as you dynamically link to it it doesn't taint your own code. This is a story about the pain caused when lawyers get in the way of writing code.
It turns out that the LGPL, as it stood, wasn't restrictive enough for the FSF's ideology. You can't have freedom without a lot of restrictions (apparently) and so they added a load more to the venerable LGPL 2.1, and created the new, improved, twice as restrictive, LGPL 3.0, and encouraged all GNU projects to upgrade.
One such project, which I'm directly involved with, GNUstep, did so. Then we started having problems. It turns out there's this other license that has a clause stating that it may not be used with any conditions that are not in the license itself. This is the (GNU) GPL. Version 2 of the GNU GPL is incompatible with version 3 of the GNU LGPL, and since it's viral you can't even link code under the two licenses.
That's okay though, right? The FSF has been telling everyone that they should use the 'or later versions' clause when they use the GPL, just in case they want to make it more restrictive in the future. And everyone's done that, right? Well, it turns out, xpdf didn't. And the xpdf code was extracted to form the Poppler library. And the Poppler library, in turn, was wrapped in PopplerKit, an Objective-C framework for rendering PDFs. And so, by the transitive property, all of these GNUstep apps were GPL 2. Which is incompatible with LGPL 3. Which meant that suddenly they couldn't use the latest GNUstep. By the way, PopplerKit isn't the only GPL2-only library used by GNUstep apps.
This is a bit of a problem. So big, in fact, that Debian decided not to carry the latest GNUstep, because it would have meant dropping a load of GNUstep applications from the next release. The eventual outcome? GNUstep has reverted to LGPL2.
This isn't an unusual situation, by the way. A number of big libraries, such as GNU libc (an abomination that needs to die, but for technical, not legal reasons) is having the same problem - the FSF wants to 'upgrade' it to LGPL version 3, but that will mean any Linux distro that ships the new glibc will not be able to ship any GPL 2 apps.
And people wonder why I prefer the BSD license family.