Thanks @vax2000 - might try that out here in Sydney sometime.
I recently used Bushman's 80% DEET formula when on safari in Kenya - didn't have a single mosquito bite - I was applying morning and evening. I used a similar, 80% DEET formula some years back when in remote Sierra Leone and didn't get bitten either.
Key to any formula is being really rigorous with the application. Apply morning and night, wear long sleeves and long pants, socks even. I used a permethrin soaked hat (with flaps) which kept the flies and other nasties away during the day.
For your common mosquitoes, a natural method like above would be fine. I wouldn't risk it if you're going to malaria prone areas - I'd be using the strong stuff for that