-bought a new SD card (Sandisk ExtremeIII) and tested that with gutsy -> same errors as before
-with feisty live-cd the old&new cards both work
-gutsy daily live-cd is broken, so I can't test that properly (modprobe fails, so plugging any usb-device results in modprobe hanging for some reason)
Ok, debugged a bit further:
-bought a new SD card (Sandisk ExtremeIII) and tested that with gutsy -> same errors as before
-with feisty live-cd the old&new cards both work
-gutsy daily live-cd is broken, so I can't test that properly (modprobe fails, so plugging any usb-device results in modprobe hanging for some reason)
so, no idea where the bug is..