This is the sort of thing that may bite people in the arse, and the reason you shouldn't really use int/char/etc for your variable types.
Up 'till now it hasn't mattered, but it may do with the Due. Of course it has more RAM so you may not notice of you're arrays double in size 
@giantsfan3
(1) I guess series resistors would help with the 5v inputs to the ARM, it's not my preferred method though, I would consider that more of a cover your arse measure to limit the current in case of a stuff up.
(2) Dunno, price I suppose. Arduinos are not designed to have robust IO and that's fair enough. It may be though that the Due will be placed in harm's way a lot. Jantje seems happy that his shields will be OK so maybe it's not really a problem. But how many users can analyse that?
I wonder how many of the UNO Based tutorials would cause damage to the lower current, lower voltage Due ?
This is the sort of thing that may be a problem, a simple high-side switch to 5v and poof.
Rob