Hi Joyent!
Qemu seems to be broken when configured without --enable-debug option. It is broken for me on two different machines one with dual E5620 CPUs the other one with single i7-2600K CPU.
The easiest way to replicate the problem is to try booting 64-bit CentOS 6 iso. It is booting OK when qemu is configured with --enable-debug. It fails to boot when Qemu is compiled without this option. See the screenshot here: http://i.imgur.com/3oAkc.png
Please fix! :D
Andrzej