Hi,
I also have problems with the new firmware -- but also with the current kernel. But I guess it's not the same problems as you describe them: I used the SD-Image 13-06-2012. It boots fine. But after upgrading (pacman -Syu), my raspberry won't boot. With HDMI connected, I can only see some nice colors (as in
http://elinux.org/File:Debug-screen.jpg). So I simply copied the files in /boot/ from the archlinuxarm-13-06-2012.img to my SD -- and I can boot again.
Strange thing: When I only update linux-raspberrypi to 3.1.9-33 and use the firmware from archlinuxarm-13-06-2012.img, I get
$this->bbcode_second_pass_code('', 'Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in c04ddecc')
And if I only update raspberrypi-firmware to 20120729-1 and use the kernel from archlinuxarm-13-06-2012.img, I get the nice colour stuff.
Has anyone any clue about that?
I would like to try do downgrade the linux-firmware, as described by sajuuk -- but where can I find it (I mean the `outdated' version -- and it's not in /var/cache/pacman)?