I once had a very long conversation with a lawyer who specialized in open source software and was a former developer himself. Take all this with a grain of salt and don't base any of your actions on it (hire a lawyer if you need to), but what I recall from the conversation is this:
BSD/MIT licenses are GPL compatible by the way.
What this means is that developers, who are accustomed to freely copying and pasting code between files, have to do the annoying task of keeping track of which licenses are associated with each file.
And when you copy and paste between files with different licenses, you have to be sure that you're not mixing licenses that are incompatible.
As far as I understand it, there is really no problem with OpenACS having incompatible licenses within its codebase, except for the fact that developers have to be careful not to mix the code. And there is the additional issue that we claim all OpenACS code is GPLed, which is either not true, or problematic if you're including non-GPL compatible code.
The solution when you have mixed code that are not license compatible is to rip out all the code that was originally from the non-compatible license. Fun.
Jade
PS An additional thing that people have to watch out for with GPL code is the definition of "distribution". If you "distribute" modified GPL code, you have to make the source code available. There are some parts of the definition that the legal community hasn't sorted out yet. But I'm not going to get into that now.
