Steps to upgrade from Ubuntu 8.04 to 8.10:
Menu: System>Administration>Software Sources>Updates
Click the "Release upgrade" drop down menu and choose "Normal Release". Click OK to close the configuration window.
Now manually run the Update Manager and you will see the 8.10 upgrade is available. No need to backup anything. Very smooth process. Just make sure you have enough disk space to download all new packages. 5G should be enough. My total upgrade only needs two clicks to confirm the replacement of few config file under /etc I've changed. That's it. Total progress pretty much depends on your Internet speed to download 1000+ new packages...