There are quite some rumors about what's going to happen on tuesday, September 9. According to Ars Technica, it is somewhat likely that not only iTunes 8, but also iPhone firmware 2.1 will be released.
What we do already know is that it will bring some improvements in the iPhone 3Gs GPS features (which is mostly interesting to developers) that will likely enable developers to bring turn-by-turn applications to the iPhone.
So, will it be the big day? Will we see turn-by-turn very soon, after all?
Well, we will know, but not before Tuesday, I guess.