I've made a detailed spreadsheet on Excel that calculates an after tax, after superannuation cash pay with dozens of variables.
It's complicated as you have to consider things like the amount of leave you get...
$12 is a bit rough most of my realistic calculations give me something closer to $13, 13.5 depending on how much leave, overtime etc you provision.
About 14 at least I guess for new starters this year assuming they'll get what I think they'll get.
But again you still really can't compare to say, your mate earning $20/hour casual in hospitality or something as your derived hourly figure can't possibly take into account things like free wireless internet cards, laptops/peripherals, amex, phone plans, stationary, booze, parking and other perks which you would never get on a casual job..
Not to mention that any casual job of any form is unlikely to pay you attend the sheer amount of training/development days as you get exposed to at some companies.