As someone that runs a website, without CAPTCHAs I'd be fucked.
There are bots that can automatically register on a site, then check the email account for the activation link, in order to start spamming, so that's not a solution.
The newer 'flash games' e.g. 'out of 5 objects, put the drinks in the cooler' are an interesting solution, but that probably still won't work for people with accessibility issues.
Moderation can work on sites like slashdot, but on lower traffic sites not so much, and the signal to noise ratio will be awful.
If Australia pass this and actually clamp down on 'offenders' it will do more harm than good as the only recourse webmasters will have is to not allow people to register/interact with the site as the cost of cleaning up spam will be too high.