Google Apps based application

[eluser]Unknown[/eluser]
I am thinking of developing a Google Apps based application. I have been working a lot with CI 1.x versions and then paused a little. As of today CI 2.x is the most recent version and all CI-libraries/wrappers (for non-CI libraries) so far did not deliver the "simplicism" I am looking for.

Question:
Has anyone already used CI to create a Google Apps (Marketplace) targeted application? Probably with some demo/extracted code? Especially the Open ID/single Sign on is making me some headaches.