Very nice script, however I have some suggestions:
Perhabs you can use ZIP packages? I have no idea if there's a way to pack/unpack ZIP files with scripts, but you can look for it.
Don't use toasts to notify the backup status. I tried to backup and it made my Messenger crash. What about a status window, with progress bar and description? Maybe you can also add a Cancel button there.
If you need help with that, just ask me on WLM.
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