This week I wanted to upgrade our SharePoint 2010 RC environment to the RTM version. Unfortunately I found out that an upgrade was not supported by MS. Also a database detach and reattach to an RTM installation would not work :-(
But what about our data and site structure?? It is not much, but like any other person in IT I am lazy by nature: Don't want to do anything unless it is necessary :-)
As a test I created a site collection backup using stsadm of the site collection, reinstalled our environment with the RTM version of SharePoint 2010 and performed an stsadm restore. And it worked!
So if you want to upgrade from RC to RTM, but would like to keep your data, use stsadm backup/restore!!