Don't flame me for this...
I think Apple will announce a more substantial iPhone hardware upgrade before Christmas. I know this is against their usual schedule, but I think the reason they held back on a lot of features was because of timing. Given that we are in the middle of a recession, people (average people) aren't going to spend large amounts of money on a new device that has little new to offer. But, during Christmas time, people will spend a lot more money on something, especially something with a lot of new, neat features. 3.0 will give customers and developers a lot of what they've been asking for for free. So in my opinion, I don't think it makes sense to upgrade from the 3G to the 3G S.