P.S. if anyone replies saying that it doesn't matter because disk space is cheap, I shall be forced to nominate you as Linaro sysadmin for this
cycle.
Ha! :) Only for this cycle?
I don't quite understand your maths there; if you look at the Ubuntu ARM images they are 540MB for netbook and 200MB for headless (compressed). So at 6 boards to support that's ~4.2GB/month or ~50GB/year which is a lot less scary.
The Ubuntu Images have an extra bit that happens on first boot where it
expands itself to consume your entire SD card.
-Paul Larson