I've got a couple and one of them has a number 1 ranking for a pretty competitive term.
If it's a good generic name that's in demand, i wouldn't care if it was a .net.au
From what I gather most domainers dont like them as much as a com.au but I guess it depends on what you want to do with them.
BTW this question would be better asked in the general questions or newbies area of the forum (also do .net searches of threads on the forum). This area (marketplace)is reserved for sale of domains.