Well, I got things working again. My rain dance was as follows:

Remove all Qt libs from the device
Update Ubuntu install (latest karmic updates)
run qmake from scratchbox terminal (rather than letting ESBox do this)
make clean
reinstall Qt on the device

Now things work. I think I may have had a version conflict between the Qt on the device and the version in scratchbox (mix of 4.5 and 4.6 beta maybe..?)