I actually did manage to fix it. Which, as you say, involved serial. I got a CA-42 cable working that I never did get working with my Dockstar, probably because I was doing it wrong. I have another CA-42 cable coming so I can mess with that. I plan to install openwrt there however, in the flash. I've always found USB booting/rooting to be flaky on my Dockstar.
Sadly, the Arch Linux ARM install instructions (which I followed scrupulously) and revert instructions did not work on my unit. Perhaps that's because none of my USB storage devices are ideal. I did manage to get Debian working by googling around over there and cobbling various instructions together. None of the available instructions there were complete either, so I wrote this:
http://hyperlogos.org/blog/drink/Debian ... -V4-MobileI don't mean to imply that Arch Linux ARM is bad or anything, only that it's currently a bad idea to install it on the Pogoplug Mobile by following the instructions here on the website. As I got Debian working I lost interest in figuring out how to fix it, sorry. I haven't yet tried booting Arch from SD card with this u-boot, but I could give it a go if there is any interest. If there's anything I'll need to do to Arch beyond setting the root device intelligently, if I even need to do that, let me know. I have set it to /dev/mmcblk0p1 or whatever
via bootparams in u-boot (see link above) as the debian setup mounts root from /dev/root by default -- why change?
I'm not interested in changing u-boot or many u-boot params, but I'm happy to reboot with other SD cards (of which I have a handful) loaded with Arch, and I have a recent download of the tarball. So if someone would like to see some quick testing, I have the magical picocom installed and so on and am willing to boot some other filesystem images, maybe even a uart-mode u-boot.