LGPLv3 is the latest version of the GNU Lesser General Public License. It follows the successful LGPLv2.1 license, and was released by Free Software Foundation as a counterpart to its GNU General Public License version 3.
The goal of the GNU Lesser General Public Licenses is to provide software that can be used by both proprietary and free software. This goal has been successfully handled so far by LGPLv2.1, and there is a multitude of libraries using that license. Now we have LGPLv3 as the latest, and the question is how successful is LGPLv3 on this goal?
In my opinion, very little. If we assume that its primary goal is to be used by free software, then it blatantly fails that. LGPLv3 has serious issues when used with free software, and especially with the GNU GPL version 2. Projects under the GPLv2 license violate its terms if they use an LGPLv3 library (because LGPLv3 adds additional restrictions).
What does FSF suggest on that case? It suggests upgrading GPLv2 projects to GPLv3. That's a viable solution, if you actually can and want to upgrade to GPLv3. At the GnuTLS project, after we switched to LGPLv3, we realized that in practice we forced all of our GPLv2 (or later) users to distribute their binaries under GPLv3. Moreover, we also realized that
several GPLv2-only projects (i.e., projects that did not have the GPLv2
or later clause in their license), could no longer use the library at all.
The same incompatibility issue exists with LGPLv2.1 projects that want to use an LGPLv3 library. They must be upgraded to LGPLv3.
In discussions within FSF, Stallman had suggested using the dual license LGPLv3 or GPLv2, in libraries to overcome these issues. That although it does not solve the issue with the LGPLv2.1 libraries, is not a bad suggestion, but it has a major drawback. The projects under the dual LGPLv3 or GPLv2, cannot re-use code from other LGPLv3 projects nor from GPLv2 projects, creating a rather awkward situation for the project.
So it seems we have a "lesser" kind of license for use by libraries, that mandates free software project authors the license they should release their projects with. I find that unacceptable for such a license. It seems to me that with this license, FSF just asks you not to use LGPLv3 for your libraries.
So ok, LGPLv3 has issues with free software licenses... but how does it work with proprietary projects? Surprisingly it works better than with free software licenses; it doesn't require them to change their license.
Nevertheless there is a catch. My understanding of LGPLv3 (it is one of the hardest licenses to read - as it requires you to read first the GPLv3 remove some of its clauses and then add some additional ones) is that it contains the anti-tivoization clause of GPLv3. That is, in a home appliance, if the creator of the appliance has an upgrade mechanism, he has to provide a way to upgrade the library. That doesn't really make sense to me, neither as a consumer, nor as someone who potentially creates software for appliances.
As a consumer, why would I consider the ability to only upgrade the (say) libz library on my router a major advantage? You may say that I have additional privileges (more freedom) on my router. It could be, but my concern is that this option will hardly ever happen. Will an appliance creator chose a "lesser" GPL library when this clause is present? Will he spend the additional time to create a special upgrade mechanism for a single library to satisfy the LGPLv3 license, or will he chose a non-LGPLv3 license? (remember that the goal of the LGPL licenses according to FSF is to use them in software where proprietary, or free of charge alternatives exist)
So overall, it seems to me that LGPLv3 has so many practical issues that actually make its advantages (e.g. patent clauses) seem irrelevant, and I don't plan to use it as a license of my libraries. I'm back to the good old LGPLv2.1.