Created attachment 44703 [details]
dmesg output from a successful attempt
When booting up Xorg server 1.9.2 with xf86-video-ati-6.14.0 and kernel 2.6.36-gentoo-r5 (distro-patched kernel, but the same problem doesn't appear in 2.6.35-g-r12), as soon as X starts, my monitor goes into DPMS powersave and I get backtraces in dmesg.
A Gentoo developer suggested booting with kernel command-line parameter "radeon.agpmode=-1". This didn't help.
I've attached dmesg output from a successful startup with 2.6.35, and will attach dmesg output from failed startups with and without agpmode=-1 momentarily (looks like only one file can be attached at bug creation time).
Created attachment 44704 [details]
dmesg output from a failed attempt
Created attachment 44705 [details]
dmesg output with radeon.agpmode=-1
that kernel doesn't have KMS enabled which is probably not what you want.
Oh, the two versions listed are those declared as ostensibly "stable" by my distro, but 2.6.37 fixes the bug.