I looked in to neo4j the other day, but was put off by the combination of the AGPL license (which, as I understand it, makes it impossible to use for any commercial purpose since you are required to GPL any software that so much as talks to the database) and a lack of any indication of how much a commercial license would cost on the web site. I know this is how "enterprise" stuff works, but personally I have a strong aversion to evaluating software when I have no idea how much it would cost should I chose to use it - that's one of the reasons I like open source.
