I'm not in favour of compulsory voting myself. I teach kids - secondary school and university - and most of them are simply not well informed at 18 or even 21 to cast an informed vote.
There are exceptions, and I think they should have the right to vote. But forcing them to the ballot box basically teaches them that it's OK to vote without thinking.
And that just leads, long term, to a less informed electorate forced to vote.
But it looks like its here to stay. The Labor party loves it - in my view, because they tend to get most of the less informed votes - people who think 'Labor is for the working man', and kids who haven't yet learned that just because something sounds good doesn't mean it actually works.
It's only advantage that I can see is that it does tend to diminish claims that a government doesn't have a mandate in some instances.