I think I was able to do that. I also think it was through iTunes as well, I may have to investigate a bit and review it; but I think I remember saving data files not just music from it.
The reason I believe this is possible is because Garageband supports uploading the garageband files to the Mac version of Garageband (and also by relation, Logic Pro) for further editing. You can't really do that without an export function through something like iTunes, at this time.