@freakazoid I heard a story that in Ireland there is a tradition that people will spoil their ballot to show discontent. The number of spoiled ballots is then reported on the news. So there'll be people who vote and purposely spoil their ballots.
The story goes on that when they introduced digital voting they made it so that everyone could have a correct ballot, upsetting a certain class of voters. They then had to introduce a "spoil" button.