The only really reliable ways to back-up the Tab are either 1) Titanium Backup (and you CAN use dropbox, if you don't want to store onto the SD card... but if I'm not mistaken, it still needs space on the SD card to store it even if it's temporarily). or 2) ClockworkMod (after converting to ext4 from rfs)--but definitely needs the SD card. Alternatively, mind you I've never done this though, I think you might be able to use adb to create dd images on the SD card, then transfer them to your PC.