There are issues with backing up 1.9 courses to 2.1. I haven't tested everything, but have found issues with lessons, online assignments, and offline assignments.
Submitting online assignments, single file, and advanced uploading works.
Grading of assignemts mostly works except the teacher is showing up to be graded. I suppose this could be someone else changing settings.
More details in the tracker. http://tracker.moodle.org/browse/MDLQA-944
I challenge everyone who went to the Moodle Moot in Helena, Montana, USA to do some QA.
Go QA!