The blocking list at dnsbl.net.au has announced it is winding down. As noted in a February 25, 2009 posting on its website, "Please note that as of Wednesday, April 1, 2009 the DNSBL.NET.AU blacklist will cease to exist."
As of this writing on April 29th, 2009, I do still see active entries when querying via DNS, but I assume that these are likely to go away soon. If you utilize this list, I'd recommend removing it from your MTA or spam filter configuration.