For Italy, definitely go with local SIM. They have some of the lowest prepaid data prices anywhere, with good fast networks, usually better than the Wifi offered at many hotels.

It is complicated though, as you have to get a codice fiscale to get a SIM.

Info. at prepaidgsm.net.

It sounds like iPhonetrip would be competitive for France and maybe Spain and when you're going to more than one country.

But for a single country with a competitive mobile market like Italy, you can save a lot of money, probably get away with 20 Euros or so for a couple of weeks.

iPhonetrip would be more useful too if you can use their SIMs on Mifis to get multiple devices online, which is what XCom Global offers. XCom appears to be using local SIMs though so if you go to more than one country, then it becomes way more expensive.