All of my mailboxes have been inundated lately with flyers announcing the new features of the U.S.P.S. Priority Mail system. This includes notificiation as to wether your package will be delivered in 1, 2 or 3 days with the service. They are also adding insurance of $50-$100 on Priority packages at no additional charge. You can read all about the changes here.
The updates come with snazzy new packaging too. The packaging remains free, but remember that it is for Priority Mail use only. The post office has been known to inspect packages that they suspect are in violation of that policy, even if you paint the box a new color or wrap it in paper. You can certainly reuse the packaging to send another parcel at Priority rate, just don't try to ship it First Class.