With Plasma released under a plain GPLv3 licence, there are a few problems that need to be addressed. Sooner is better, especially since Microsoft might not be too happy about having some of their code inadvertently released as GPL.
The first part of the problem is where Cyan used 3rd party code in Plasma under a licence like the MIT licence, but then copy-pasted a GPLv3 header on all the files when the code was released.
In particular, PubUtilLib/plWinStrBlock/strblock.h and PubUtilLib/plWinStrBlock/strblock.cpp are copyright by Microsoft.
Also the files in FeatureLib/pfStackTrace (such as pfStackTrace.cpp, pfPrintStackTrace.cpp, and pfMapFile.h) are copyright by Jani Kajala, who also demands that the copyright notice be made visible in all supporting documentation.
There's also two classes in PubUtilLib/plWndCtrls (basewnd and webhost) that have the following comment:
Stolen from: http://www.mvps.org/user32/webhost.cab
No copyright notices, so I assume it's public domain -Colin
I'm entirely sure that Cyan had no intention of violating these licences when they released the code (and as far as I know, both licences allow the code to be used in GPL software). The problem is that they've pasted the GPL licence on top of the existing licences. It's always best to be careful around the GPL, as it has caused problems in the past for companies (like the infamous DLink case).
The next issue in licensing is that Cyan didn't add provisions for linking against PhysX or the 3DS Max SDK. It's also a bit unclear whether a special clause is needed for linking against OpenSSL (on Linux I don't believe it is, but for Windows it might be).
Without these provisions, nobody can (legally) distribute a compiled binary. Of course, it's very unlikely that anyone would try to stop you, since that would be entirely against Cyan's interest in open-sourcing the code. But technically, it is still a violation of copyright to distribute any compiled Plasma code.
This was originally mentioned months ago, when the code was first released. The problem now is that in order to change the licence to add these provisions, Cyan needs the permission of everyone who has contributed code to the project. That number is starting to grow, as can be seen on the contributors list for the GoW fork.
At this point, it seems more likely that PhysX will be stripped out and replaced with Bullet before Cyan has a chance to update the licence. This solves the problem for the client, but the Max plugin is still a problem because it links against the Max SDK.