If you don't vote, you get fined. I failed to vote in my council elections once, and I cheerfully paid the fine (about $50), because I totally agree with the idea of compulsory voting. IMHO, in a democracy, voting isn't a right, it's a duty.

It does make the political landscape quite different, I think. Instead of wooing the extremists (which in a voluntary-voting democracy are the ones most likely to vote at all) the politicians have to woo the moderates (the "swinging voters") because they are the ones most likely to change their minds about who to vote for.