I asked some of my friends and it seems few of them know this 'Medicare levy surcharge' thing. Below is the explanation from ato website:
What is the Medicare levy surcharge (MLS)?
Individuals and families on incomes above the MLS thresholds, who do not have private patient hospital cover pay MLS for any period during 2007-08 that they did not have this cover.
We calculate MLS at the rate of 1% of your taxable income. The MLS is in addition to the 1.5% Medicare levy.