MLHmptn - 10:00 am on Dec 24, 2012 (gmt 0)
I am going through this process right now and it was a nightmare! We just received fiber into our building and the servers didn't like the IP migration wizard (64 ip's) within cPanel...long story short I gutted the server after backups and upgraded to CentOS 6.3 from 5.8 figuring if there was ever a good time to do it, it was now. Don't exactly understand how cpanel's ip migration wizard just annihilated our zones, ip setups, resolvers, and whatever else I didn't know about.
I am sure hoping the 2-3 days of down time won't destroy our rankings. To make matters worse I have two domain registrars that haven't been open, nor had support until tomorrow so our main domain (and a few others) is sitting in limbo until tomorrow morning until we can update the NS and A records.
Long story short....NIGHTMARE but the fiber sure is SPEEDY!