SQLI just released a book (in French) about integration of Google Apps in Entperprise Information Systems:
Intégrer Google Apps dans le SI

Convertigo is mentioned in the "3rd-party extensions" chapter.
We have more and more requests about integration of Google Apps with legacy business applications using Convertigo. We are working on the packaging of a Google Apps framework for Convertigo.

[img]http://sqliconsulting.files.wordpress.com/2010/09/livre-google-apps-couverture.jpg?w=250&h=356[/img]