David Farley has written a book about the history of the holy prepuce. (This kind of post is both a Friday frolic and what happens to your head after an all day faculty meeting). He is interviewed for Interfaith Voices (about 38 minutes into the program).
The santissimo prepuce has a long history that belongs to the history of holy relics that began to thrive in the 11th Century. From an angel's hand it passes to Charlemagne and thence to an Italian village, Calcata, near Rome. It was stolen in 1983.
David Farley concludes that the relic has the power for belief and hope and that this is its most important quality. An uncut version of the interview is here.