As you probably know (if you are interested in the Enterprise Linux market), Red Hat released earlier today 5.6 . So automatically some CentOS QA team members started to discuss about that in the appropriate IRC channel. As CentOS 6.0 isn't (yet) released nor ready, the discussion was about putting 5.6 build & release as priority number one or not. Karanbir on his side asked on Twitter about thoughts on the matter, and a discussion was started too on the centos-devel list about that topic. My personal opinion (and shared by some people too) seems to give 5.6 the priority for quite some reasons :

• The centos 5.x install base is there while there is (obviously) no centos 6 install base.
• So those people having machines in production, faced to the net (, etc, etc, ...)  would prefer having their machines patched and up2date (security first !)
• People running CentOS 5.x on servers and willing to install php53 packages, now officially included
• On the build side, the el5 build process is clearly identified and known since 2007 : packages with branding issues are already identified and patches/artwork is already there, meaning that it will be probably (no, surely !) faster to have 5.6 out of the door than 6
• Same rule for the QA process : people from the QA team can "blindly" focus on their previous tests, and just have a look eventually at some newer packages (a few, like php53 but not that much in comparison with el6)

Please notice that it's still my personal opinion on that question and isn't the (to be defined) official CentOS position.