I am using an 8 GB SD card. It is working as checksum after the copy is reported to be ok.
I believe it is a problem with either Debian itself or the Raspberri hardware. Lots of users suggest it is the fault of some keyboards (curiously mine works both under Windows and OSX (PPC)). I wrote an Archlinux image to the same card and could get to the login screen, but when I plugged the keyboard, everything went to guru land (well, kernel panic land).
So I am clueless, maybe it is some hardware bug of the Pi?
I am a bit dissapointed as this was my first day playing with it
