The are two issues I've been running into when upgrading to 9.0 from anything. When taking a backup of SBO-COMMON through the upgrade wizard it will crash the upgrade and not show any errors. You can get around it by taking a manual backup of the common database and then telling the upgrade wizard to not back it up.
The other is when upgrading the client software. Instead of upgrading it automatically after the databases have finished it will hang for hours. Instead I've been uninstalling it, wiping any leftover folders out, then reinstalling it from B1_SHR.