[merlyn]

I've noticed this too. It definately is by product.

Since I buy lots of weird stuff, my delivery times are all over the place. Some items can be obtained same day (if I buy enough $$), or overnight. Some "Prime" sales can take a week to ship.

I also see different geo areas get targetted for certain days. Like my home address tends to get things Wednesday and weekends. My office building gets things on Fridays, and Amazon knows enough that weekend delivery doesn't work.

So to me, it seems like they are aiming for an "average", keep certain things close, make people happy with real short delivery, but if you get weird stuff, you are probably going to be less happy overall with longer shipping delays.