I just bought a 2GB SD card from PQI for $22 after rebate of $16 !!! Damned good deal. It's a 150x card.
Can't say as I notice much/any speeding up of transfers in the Zaurus, but it allows for faster transfers in the PC card reader.
If Moores Law holds for the immediate future, I reckoned we should be able to get a $22 SD card that holds two Terabytes in about 10 years ;-)