all i have are these Kingtson SD 512mb cards.
Going from memory, Kingston cards are the most reported to not work with the JB
I thought part of the SD spec was that ALL SD cards were supposed to be MMC compatible, and support SPI mode.
Since the only info ever publically released (and appearently pulled) about the SD card spec was a terse white paper, take anything you've heard with a grain of salt.
Is there definitive info somewhere?
Check on the http://OESF.org/forums , which is as close to 'definative' as you can get without signing an NDA. The Sharp Zaurus is not compatable with 2GB+ cards using the normal drivers, however, a closed source driver has allowed newer 2GB+ cards to work with the Zaurus. There was also talk of a GPL SD card driver with 2GB+ support being developed by commision of makers of the TomTom GPS. Appearently, there is a SD card driver in some of the newer Linux kernels, but only supports 1GB and below.