If its just a matter of "weeks" then wait. When it becomes "months" then you have to ask yourself how serious you are about upgrading.
Mere weeks and saving a ton of dough, I'd wait. I've got my 1710 so I leaped, but that was months ago. And I knew I'd take the cash it in buying Merom later and upgrading.
Be aware, that everyone and their brother/sister is gonna be ebaying Yonah cpu's when Merom comes out. That means a very poor return if you understand how that works. So don't plan on covering most of the cost of Merom by reselling the old chip. Either be ready to pay up and take the loss or wait.
If I were in your shoes I'd wait. By first week of Sept, or about 5 weeks, you are likely to see zillions of Merom ads start flying up.