First - the Baby Bonus and Maternity benefits are different things. One is being introduced now, and the other is being phased out. The BB was introduced to INCREASE the population of Australia. It WAS meant as an incentive for increased birth because as a country Australia is struggling to pay for itself (particularly in terms of welfare) and it's only going to get worse as the tail end of the Baby Boomer generation gets older.
I don't have stats on hand right now, but I'm going to go out there are say it actually didn't increase teen pregnancy beyond normal rates of rise. As I said, I can't back it up right now, but I'm positive I've read it somewhere.
And the difference between the BB and Maternity is (well for me) $26 over the 16wks. I am thankful for the maternity leave benefit. AND your employer pays it and claims it back from the government, so TECHNICALLY you're not getting a handout from the government, your employer is

that and the reason a lot of working mothers don't have kids (or put it off until they are in their 30's or 40's) is because they can't afford to stop working. I have a girl at work who had her son just before xmas and is coming back to work end of May because she has too. Does this mean she shouldn't have had the kid? Not really. If we all put off having kids until we could afford it we (the full time working population) would never have kids, and the future of Australia would be left up to the dole bludgers (no thanks!).
God help this country when the baby boomers all stop working. Yes there will (or at least should) be a lot of jobs opening up, but things will come to an abrupt halt for a little while, and we'll see more caravans on the road (oh yay!).