If you are like me and cant wait 5 days to install the new Ubuntu 9.10 karmic Koala, you can upgrade with a single command and install the latest release candidate.
sudo update-manager -d
The release candidates by itself are stable enough to be installed on your workstation, as they are the closest to what the final release will end up being like. However you are advised not to do so if you are not very familiar with troubleshooting and recovery system if something where to break down during the upgrade process. Even when you upgrade to the release candidate Ubuntu does a clean upgrade to the final release when it is released to the public.
I installed it on a spare Ubuntu partition I use for testing purpose. The install process itself was a breeze but there were some minor stability issues with release candidate, which should be sorted out before the official release.