Right, the sad truth is we looked at Neo4J a long time ago and we decided against it because of the licensing. Not because we are cheap, but because we knew that the licensing would keep it from being a mainstream product, and the reality is as a developer you have to invest your time where the money is, and that is always where the momentum is. Toolkits and frameworks like Struts or jQuery succeeded because of their licensing not in spite of them.

I like to take Ext.js as an example they where a front-runner in the JS toolkit space early on and to many looked like they had it in the bag. So much so that one day they switched their licensing to a GPL / commercial model. Overnight it seemed they went from the heir apparent to a footnote in the JS toolkit space.

Licensing has a lot to do with technical selection when it comes to application building blocks, I see Neo4J as a different but in the end similar building block and therefore the licensing is extremely important to me. I think they have a good piece of technology, that due to licensing will most likely leave it in the niche market, therefore I chose to not invest my time in it and learn one of the more liberally licensed alternatives, which since that time have gained momentum. On a purely technical level, I would have chose Neo4J so the moral of the story is that licensing plays an equal part in technical selection.

To be clear, I am not telling anyone how to license their hard work, just offering some insight into how some developers chose the technology to invest their time in.