Of the big international sites moving into the Aussie market, I think Lavalife has been at it the longest. And eHarmony has been going for a while, with a lot of ad exposure in recent months.
Then earlier today I saw a television advertisement for POF (Plenty of Fish). That was surprising because it is still basically a free site (although you can pay for an upgraded service that gives you even more options and visibility).
The fact that they've decided to run very expensive TV ads here confirms that POF -- like the big paid dating sites mentioned above -- is doing very well indeed in this country. To use their own metaphor the Australia dating pool is clearly a long from being overfished and there are clearly still many thousands of members yet to be hooked!