I was thinking the same thing. Way to be a good co-worker! You are giving a new person a whole day to learn what you worked on for 5 years? How very kind of you. I can only hope the person you are taking over for (or working with) shows you the same courtesy.
I agree with this. I have had customers running RHEL and CentOS and there have been a few times where CentOS does not keep pace with RHEL (most notably with the RHEL 6.x release). Support for issues is one thing but if the OS is not patched because the vendor, in this case CentOS, does not push them out then what recourse do you have as a CentOS user? You didn't pay for it so, to be blunt, "Sucks to be you." You take your chances when you choose CentOS for production environments.
I would recommend Arch Linux ( http://www.archlinux.org/ ) if you are comfortable with installing from a text interface and partitioning your HD yourself. I have found Kubuntu to be a bit rough around the edges when it comes to the KDE implementation where as Arch has been rock solid for me. Arch also is bleeding edge so you can enjoy 4.6 right now without PPA. Just a suggestion. Perhaps Arch will provide the best KDE experience since you are trying it again after being away for a while.