I have been able to boot a kernel compiled on ubuntu 9.04 using tftp and u-boot on the sd card that came with the qsb.
I followed the below instructions and built a zImage kernel and u-boot image on an ubuntu 12.04 machine. u-boot runs but it complains about uEnv.txt and the zImage. Should these instructions work?
EDIT: I converted this zImage to a uImage with the mkimage tool and it booted ok, so the zImage is OK. However my question still remains.