If you are looking at a handheld solution, the new 24-85 lens being released with the D600 might be a good alternative (and a lot cheaper). It won't give you f/2.8 - but it does have VR and a much lighter weight with a compact size. It's probably a good choice for street photography. You might pair it with a fast prime.
I have the 24-70. It's a fantastic lens. But it is heavy.
Another good alternative is the 16-35 f/4 VR if you want something wider. It's also light weight and easily carried.