After a few days playing from SD card I've gone berserk today and installed arch linux directly on emmc
Pretty painless actually, just booted from USB, created clear GPT on /dev/mmcblk0, added 3 partitions (kern-a/kern-b/root, I've managed to do it with gdisk only, although attributes were a bit complicated), copied rootfs content from SD to new ext4 root, built kernel image with root=/dev/mmcblk0p3, wrote it to mmcblk0p1 and p2, and voila
it actually booted! I strongly recommend copying content of original chromium rootfs (ROOT-A for example, I think it's /dev/mmcblk0p3 in chromeos), it can come in handy if you'll need to rebuild kernel. If copied correctly it's actually possible to chroot into it from arch...
Power management mostly works, the only problems I found so far is disabled display after X DPMS power saving (the only way to turn it back on was to get in over ssh, run pm-suspend and wake the machine up with a key press), and a bit funny behaviour of upowerd when I unplug the adapter when battery is full (it keeps on showing adapter connected, but it works correctly if I plug power back in and out after a while when battery power goes a bit down).
Display brightness plugin in xfce4 works perfectly, and as I had to disable DPMS in X I have added a few lines to /etc/acpi/actions/lm_lid.sh to turn backlight fully off/on on lid close/open.
Touchpad works fine, it's a bit big for my taste and even after I enabled the option to turn it off while typing, I still manage to activate it accidentally when I don't press any key (found no fix yet for having big hands). Right-click works now with two-finger-click (and middle with three-finger), see http://blogs.arm.com/software-enablemen ... hromebook/
Keyboard had to be tweaked a bit with loadkeys and xmodmap to get pgup/pgdn/home/end/delete working in both X and consoles. I haven't done anything about capslock yet, not really that important to me, but shouldn't be a problem to get it working on the funny search key. I'll have to buy some keyboard stickers, at least for F1-F10 keys. Also, I use US layout on a GB-printed keyboard, so there are some more keys out of sync with their labels.
I'm running X with xf86-video-armsoc driver from alarm repository, it's pretty stable (haven't tried hdmi output yet). It has no acceleration, at least for video playing, so 720p h264 2.5Mbps videos are not really playable, much less full-hd.
Sound was mostly easy, at least on speakers. I had to play a bit with alsamixer to get correct combination of mute/unmute on quite many channels available. I haven't found a way to control speakers and headphones volume separately, actually it's not even possible to mute the one without the other the usual way. The only thing I can do is to manipulate mixer controls "Left Speaker Left DAC1", "Left Headphone Left DAC1" (and corresponding Right/Right alternatives), these are just on/off switches that allow me to turn each channel on both headphones and speakers on/off separately, so I can effectively turn off speakers and listen on headphones only.
I'll have to check chromium-os and exynos arndale board source codes for any hardware video decoding drivers, those are a must for any serious video playing, but other than that I have a pretty fully functional little notebook