I think earlier for short periods of time before they get to that separation anxiety age (which just so happens to co-incide with the end of maternity leave provisions!! Although, I think the Rudd govt has it gazetted that maternity leave will soon be 24 months, yay!) probably does help when the time comes to do full days in childcare, because they get a chance to get to know their carer before they develop that 'stranger danger' radar. If you're worried you could try a couple of 1-2 hour sessions and see how it goes. It might either ease your mind or help you make up your mind...

DS didn't go to childcare until almost 2 but he did have short stints with my mum which started from a young age and that was never a problem as he was familiar with her.