FYI, it cuts both ways - when doing Postgres work on ACS 4.6, I don't get to use OpenACS code, because it's GPLed, we don't own the copyright on all the OpenACS code, and the GPL is intentionally incompatible with pretty much all non-GPL licenses.
As far as I can tell, ideas discussed on bboard are fair game (specifically, dealing with connect by - eventually I'm going to benchmark nested sets vs. precomputed sort keys and pick whichever is faster); I'm just avoiding code (anything that would go into a tarball distribution).
It's worth noting that you actually have more options under the MPL derived license than under the GPL - if you want to release a software product that uses the ACS, you can choose what license to use for your code. Previously, it was all GPL only. Because of this, I was personally thrilled when this license was selected (I had no part in the decision, but I think it's a great one).
I'm surprised that none of you have run into business problems dealing with GPLed software. I have personally seen a client refuse to use the ACS because they were convinced that the GPL virus clauses could cause them to make all of the content (pictures, mostly) they posted on their ACS site be GPLed. It was an absurd concern and I got to brief them on why they were wrong (derivative work blah blah blah), but their lawyers were never satisfied - they had heard the GPL was infectious and couldn't get beyond that. I suspect not having the virus clauses will make sales a bit smoother and open up new options *for everyone* in product development.
