Dealing with International orders every day at work I can tell you that any parcel that is sent unsigned is an absolute nightmare. Usually it goes by such a circuitous route and through so many handlers that don't need to account for it, that anything half interesting goes missing. Objectively I would say the "loss" rate is probably about 1 in 4 parcels that we send via this method, and the good old Royal Mail being what it is means that businesses cannot claim ANYTHING for parcels that are not sent tracked.
TBH the tracking I've been able to do with the numbers assigned to USPS parcels haven't had lots of detail. just basic info like:
-Recieved at Phoenix, Az processing center at 13:30 on 9 May 2013
-Dispactched from Phoenix, Az processing center at 00:00 on 10 May 20013
-Recieved at Pensacola, Fl processing center at 14:30 on 10 May 2013
-Disapatched form Pensacola, Fl processing center at 00:35 on 11 May 2013
-Recieved at Crestview, Fl processing center at 06:40 on 11 May 2013
-Sent out for delivery from Crestview, Fl processing center at 08:00 on 11 May 2013
-Delivered at 14:47 on 11 May 2013
Usually not that prompt but you get the idea. No real details