Now don't go bugging people asking when CentOS 6.7 will be out. "When it's ready."
In upgrading from RHEL 6.6 to 6.7, I did find that I had to disable my 3rd party repos (elrepo and epel) in order to avoid yum erroring out. Plus I did the usual "yum clean all". (I don't use the PackageKit GUI as it's been unable to complete for quite a few months without dumping core.)
Devin