At the very bottom of the above article. Says the street date is September 2nd.
I've seen it on HD DVD, and I have to say that it wasn't a great movie at all, but perhaps my expectations were too high. Nowhere near the quality of Sci-Fi classics such as Independence Day or Terminator 2, or even Bay's recent The Island which I found to be more interesting and better paced. The extras on the disc are great though, all HD releases should be as fully packed (but as the movie wasn't interesting for me, I haven't even looked at any of them yet).