You are right Gavrobere, in saying that functional consultants have a part. That part is performed in "impact analysis" project. Before the upgrade some companies (most large companies) conduct impact analysis project. This project usually goes on from 2 to 5 months. For example just recently Deloite did 2 months analysis for Rogers Canada. Main deliverables include a document listing impacts the upgrade would have on end users and business processes. Based on that green light is given to the next "upgrade project".

As far as the actual upgrade is concerned it is mainly carried by DBAs. Functional guys are on alert and come into play for testing the configuration and functionality in the test environment. Upgrading from 11i to 12 and reimplementing R12 are two different things. Former calls for impact analysis as most of the setup will be automatically upgraded, while the later calls for requirement gathering as this is a fresh implementation and you would like to restart from scratch. I thought the original question was about how to perform the upgrade. That would be covered under DBA training not functional training. These are my 2 cents.