There's a week to launch, but there are now units in shops if you can't wait or aren't buying one or whatever. Here's where I've seen them so far, and what game they have on display-
Electronics Boutique (EB Games) - Mario 64 DS
Target - WarioWare Touched (Demo)
As for where they haven't been: Toys "r" Us, K-Mart, Myer (Grace Brothers), David Jones.
They had been at EB for a while but you had to play it at the counter while you got the hard sell (which is a bit like haveing someone talk to you while you pee) and Target has also had them for a bit, but finaly got around to plugging them in.
My advice: go to Target if you want to see what the system is about, WarioWare is a much better example. Also they have them at a much better height.
Also I can only vouch for Perth, but these things tend to be the same in all states.
And if you're realy desperate to buy something DS related, Target in the Galeria has Ping Pals for sale already. Which is particularly useless as even importers have no use for it unless they have an importer friend.
I'll update this if anthing worth noting comes up.
[edit]: just in case anyone's wondering, K-Mart and Target aren't owned by the outlets of the same name in US, but are owned by ColesMyer (Myer is mentioned above). Uh yeah just some trivia I guess.