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I doubt RedHat supports CentOS unless you pay them too. My guess is they usually only support RHEL.
Well, it seems in this discussion 'support' is shorthand for 'patch and security support'. I don't think anyone was implying RH is supporting CentOS in the trouble-ticket sense. In any case, CentOS 5 will be 'security supported' until March 2014, which is a longest available right now (I think).
While I do agree that RHEL 6 is long over-due. (Especially if you use it as a workstation), in RedHat's defense, a lot of resources were invested in making 5.3 and 5.4 more competitive with recent distributions - anything from new(er) Firefox, evolution to backported network stack changes, updated drivers and KVM support.
Hopefully RHEL is right around the corner. (And with it, more blood into the EPEL project)