I just upgraded to 10.5.6 on my MBA, Mac Pro, MBP and they all are working just fine. I transferred about 750MB of data with each of my thumb drives as a test and they are working just fine. I just plug into the USB port and the thumb drive flashes four times; I open the thumb drive; then close it; then eject it by click, drag, and release to the trash can/eject icon and it flashes four times and then I remove the thumb drive..🙁