I got arch arm running off a microsd card using the base image on the downloads page, and the kernel + initrd from [ubuntu] modified with a custom (minimalist) init script to load the userspace from the arch base image. It could be easily booted from internal flash as well.
[ubuntu] refers to this post:
[Q&A] Ubuntu on the Transformer (eMMC install)http://forum.xda-developers.com/showthr ... ?t=1191141
Arch base image:http://archlinuxarm.org/developers/downloads
ARMv7 OMAP3/4 platforms
My init script (in the root of the initrd):
mkdir -p /proc /sys /dev /run
mount -t proc proc /proc -o nosuid,noexec,nodev
mount -t sysfs sys /sys -o nosuid,noexec,nodev
mount -n -t devtmpfs udev /dev -o mode=0755,size=10M,nosuid
mount -t tmpfs run /run -o nosuid,nodev,mode=755,size=10M
mount /dev/mmcblk1p1 $NEWROOT
exec $NEWROOT/sbin/switch_root $NEWROOT /sbin/init 3
I set up users and passwords by chrooting onto the arch image via busybox.
This of course isn't a complete solution yet, but it's a good starting point. Next we need to copy in all the drivers and try to get more stuff working (wifi, sound, Xorg, etc.) I haven't been able to get my own kernel based on Asus' source to boot the initrd yet.
If anybody is interested in testing or developing this further, I can post instructions to reproduce the boot image and so on. I expect a full official or unofficial port is quite possible