I’ve just completed my Mac OS X Mavericks clean install on my old trusty MacBook Pro 5,5. The update happened without any greater complications. However, I was missing all my WiFi and email passwords, although I’ve copied over my old login keychain.
Mavericks introduced a new „local items“ keychain, which should be used to store logins that are not to be synced with the iCloud keychain. If I move all my entries from login to local items, then my applications recognize the saved credentials and everything is working as before.