I would say overall the process which isn't complete yet (90%) has been pretty smooth. Because we had to recreate everyone's outlook profile it had to be highly coordinated.
If there was one pain point it has been the calendars. All calendars, even in the new profile, that you had access to must be deleted and re-added. If someone shared a sub-calendar, they must re-share it since you can't search for someone's sub-calendar.
We also had to re-add any full-access permissions that were added previously.
Finally on the calendars, if we add full-access permissions to a calendar, and then try to re-add it to our outlook client, we do not get the permissions until we recreate our outlook profile. Even after waiting a day for any sort of possible replication.
But overall, there has been very little complaining about the move with this exception.
