Before doing the upgrade, be sure to do these ten things:
- Make a complete backup including your theme.
- Perform any updates that WordPress notes to your plugins.
- Check the compatibility of your plugins. This site is useful as is this WordPress site.
- Deactivate all plugins
- Check the compatibility of your theme. This site is useful.
- If there are theme compatibility issues, check for fixes from the theme developer.
- FTP the updated files (be sure you don’t overwrite customizations).
- Perform the automatic update to 2.8 from within WordPress
- Reactivate only the compatible plugins.
- Check any plugins that were not listed as compatible or having known problems, by activating one at a time.
Of course you could always wait until 2.8.1 to be safe!