This is *incredibly* interesting to me, not because I'm a big QuickBooks user, but because I'm always interested in hearing ways that people are using Spring Social for non-Social things. For awhile now, I've thought that the name "Spring Social" may be a bit misleading and it may lead people to think that it's only good for Facebook-like stuff. Using it with QuickBooks demonstrates that it's really a more general API-connection framework--and the social network stuff is just the fun side of it.
One quick bit of feedback: It looks like the stuff in the "com" portion of the source code was generated by JAXB. Any reason why that generation isn't part of the build itself? In general, I don't like checking generated code into a source code repository if it's easily generated as part of the build.
Finally...I always like to promote any Spring Social community contributions with Tweets, a link on the Spring Social homepage, etc, etc. Would you mind if I tell the world about this?
Spring Social Project Lead