I still think that Sony ought to mess with MS a bit on the launch date.
For example, around TGS, they could announce a launch date of May 15th. MS will then plan the development of Halo 3 to get it in stores on the 15th.
Then, around mid-late April, they suddenly bump up the date and announce it will launch on April 30th. MS will be left scrambling, since the game will still have nearly a month of development left. So they'll either A) miss their launch window, or B) end development early and release an unfinished, and no doubt incredibly buggy Halo 3.