Internet plans in Australia are pretty bad. I've found Telstra to be reliable until recently. I live in Melbourne and the quality of service has been degrading for some time now, especially in the CBD. However, I was recently in a small town and the quality was excellent. Depends on where you live.
And one more thing, I've tried Optus and Vodafone - they have both been equally bad. I am stuck with Telstra because of a plan now :).