i'll second that about canberra.
sydney is fun and has plenty of touristy stuff to do. it's worth going to bondi beach, up whatever the big pointy tower thing is, driving over the bridge (it is a
marvel of engineering etc etc). stay in
this hotel if you want an incredible view of the harbour bridge and opera house
everyone says that (possibly excluding montreal) melbourne is the best city to live in in the whole world, i was only there briefly but it certainly had a very relaxed atmosphere. in may it won't be overly warm by any means.
western australia is aparently a bit scary; full of gruff sheep farmer types, so if you're in perth, don't spend your whole time looking for a mardis gras or a vibrant gay clubbing scene. one thing to note here is that in pubs, it's assumed you always want another drink unless you specifically say you don't, so it's easy to let the barmen get you hammered inadvertently (even with their tiny beer glasses), as you finish one another swiftly appears.
general hint: take a brazillion memory cards, you'll take a LOT of photos by any standards, cos everything is
weeeeeeeeeeeeeeird, from the place-names to the animals that'll surround you much of the time.