I just read on the US State Department site, the following requirement for Italy:
Those staying for more than eight days, are required to register with local police and obtain a permit to stay (permesso di soggiorno). Tourists may request an application for the permit from one of 14,000 national post offices (Poste Italiane). The kit must then be returned to one of 5,332 designated Post Office acceptance locations. Failure to obtain the permit of stay within eight days is punishable by fine. Permit requires 1 completed form, complete photocopy of passport, proof of sufficient funds, photos, copy of insurance policy, onward/return ticket, and a fee.

IS THIS Correct?

Usually your hotel or landlord takes care of this for you. It is why you have to leave your passport at the main desk for a day or so when you check in.

what Pausanias said. The hotel will either take you passport for a few hours or overnight - or will make photocopies of it. Don't freak when they insist on having your passport. Totally normal . . . .

Susan,
I also found this info close to my departure date this past March and got a little worried...but as others said...not to worry. Each place we stayed took our passport for about 10 minutes.

One thing you might want to know about though...I was traveling alone with my teenage daughter. I did have a notorized letter stating that I had my husband's permission to take her out of the country. The letter also included details about our itinerary. Don't know if you have that situation, and I had no problems, but they can occur.

susan217,
From http://italy.angloinfo.com/countries.../residency.asp

Permesso di Soggiorno per turismo: permit for tourists. Anyone visiting for more than a week, who isn't staying in a hotel, official campsite or boarding house


Henry

So this requirement could affect those who are staying in an apartment rented directly from owners, rather than an agent. I don't think this rule is strictly enforced or chased up - but of course, should we be unlucky enough to fall foul of the law (e.g. serious traffic violations), the fact that we didn't register may be used against us.