A key plot point of Expiration Date [1], Powers speaks about this item in our Exclusive Author Interview [2].
Recently I can across this entry [3] on the io9 Sf Blog [4] which details the item and shows a fabulous picture of it too - which I choose to link to rather than lift! Take a look [3] - it's a fascinating thing!
Now we just need to find the bust of Dante in which it was hidden for all those years!