Uhhhh my 64-bit ARM board with Ubuntu just rebooted itself out of the blue the other day, for no reason while I was browsing with chromium. I don't have a good feeling about this, so I swapped out the microSD with another one that has OpenBSD on it. The web browser on there isn't as fast, but so long as it works that's good enough for me. Plus I shouldn't be using those modern browsers much to begin with, and Ubuntu was letting me get used to a bad habit.
Also I removed the extra serial port definitions in my cubietruck FEX file, because it somehow was conflicting with tty0. I don't understand why because I checked all the pin assignments, etc. but it completely hosed the TX, so I could only see messages on the serial console but not type anything. That means I'm stuck using the USB<->serial adaptor, for now (until I can figure out what I did wrong).
Also I played some tetris (from bsdgames) over the serial and it was pretty fun. :-) The serial port runs slower than ssh, so there's a small bit of lag that makes things more interesting in a "retro" sort of way. Right now it's set to 115200 baud, maybe it would be more interesting at 9600.
At some point I'll need to upgrade this from 6.9 to 7.2 or whatever they're up to now. Might be better to get another SD card and do a fresh install though (plus that way there's a backup too).