One point to mention on this. On the upgrade notes it only mentions what order you should follow for the upgrade of the core components. Just remember that if you use a third party product for managing non Microsoft devices i.e. Jalasoft's Xian Network Manager then before upgrade stop the connector services for this product as it may be making use of some of the core dlls which OpsMgr uses meaning there could be a problem with doing an upgrade (I have experienced problems with one upgrade hence why I say this). I think this should really be in the prerequisites for the upgrade as some organisations out there have large deployments which use third party products in connection with OpsMgr for monitoring.