Did two upgrades yesterday with no problems.
First and ReportNet 1.1 MR1 -> ReportNet 1.1 MR3 upgrade in a production environment and then a ReportNet 1.1 MR1 -> Cognos 8 MR1.
Far the easiest upgrades I've done compared to the Series 7 upgrades.
I didn't upgrade the contentstore db, but deployed it and imported it on the new install.
Regards,
Søren