Once rebooted, I opened a Bash shell and became root once again prior to "yum install fedup"; as instructed, just to make double sure about having the latest fedup utility: yum --enablerepo=updates-testing install fedup
I allowed the fedup utility to download necessary resources (time depends on one's Internet connection bandwidth and existing software). After download process finishes, there will be added a menuentry 'System Upgrade (fedup)' to GRUB list -- in my case at the top of the list.
Accordingly, no manual intervention was required to start the fedup Upgrade to Fedora 18. It boots into a default screen with a progress bar centered. I did not touch the ESC key, so the progress bar slowly but gradually advanced to continue the software upgrade without any manual intervention from myself.
After some time elapsed (and the progress bar advanced to the end) the system rebooted by itself into Fedora 18 Spherical Cow #GNOME 3.6.2. I did not experience any difficulties. #GNU/ #Linux