OK, so I've got two PCs with Radeon 7000. One has PCI version of the card, and the other has AGP version of the card.
Before update to 4.2, I had DRI enabled on both of them, and it worked stable for me (lucky me). After update to 4.2, the PC with AGP version of the card does not load radeon kernel module anymore, and it seems DRI related options from xorg.conf file are ignored. On the PC with PCI version of the card radeon module gets loaded and everything still seems to work nicely and stable.
I remember some talk about DRI being disabled when Radeon 7000 is detected on Alpha (or PPC, not sure), and this being CentOS specific modification. Has this modification by any chance accidentally leaked into i386 packages? Or is this something that came from upstream?