You often get more information when you track with Aus Post - USPS generally goes direct from "Out of foreign customs" directly to "At foreign delivery depot" then straight to "Delivered", whereas Aus Post gives you "Out for delivery" etc. Weird that it doesn't come up there for your delivery though.
I like the Delivery Status widget by Junecloud (JUNECLOUD // software / mac os x / delivery status 5.2) for tracking - it pings every so often to check if there's an update and displays a Growl notification if the status changes.