The reason why Super Saver Shipping is free is b/c the time from order to shipping CAN BE longer. The long time someone else mentioned, 9-11 days before shipping, is part of Super Saver; you're saying "since you're giving me shipping for free, I can sit on my hands and wait while you get the other, paid shipping, orders out quicker."
Most of the time, in fact all of my SSS orders, arrive well before estimated time. But the times that they wait, I can't complain, b/c that's what I agreed to for the free shipping.
I do not know if this is the case, but it's possible their system is now taking into account where the fulfilment center is, and therefore it's personalizing it to that extent, as to when it will get to you.
And for the record, for states in which
amazon has a physical presence, say Nevada (fulfillment center) or Washington (headquarters), etc, an item sold BY amazon will have tax charged on it. I've been informed by the expert I have in my house that Sellers don't charge tax on any shipments, but if it's coming directly from amazon, if you live in a state where they employ people, you're going to be charged your state's tax (oh what fun to have 9+% tax here, ugh).