We were in Rome two days prior and two days after our cruise in October 2006. I too left all my real diamonds at home. I purchased some beautiful jewelry on QVC and HSN that looked like diamonds, but are not, but be careful....remember the idea is to go understated, not buy a large sparkler. I also purchased a small purse that hung across my front instead of having one hanging at my side. The main thing is to be observant as you would anywhere else in the world. Don't be distracted by street entertainers, men - place your wallet in your front pocket, carry cash in a couple of different places (my husband wore a money belt under his waistband) in addition to the wallet in his front pocket, that way nobody saw all our money.
Word to the wise....be sure to carry extra kleenex or toilet paper during your trip to Europe...we had to use our personal stash a number of times (especially on tours as everyone hits the same place at the same time and the various workers don't have time to refresh the toilet paper. I saved several rolls of toilet paper from home (replaced them as they got about an inch thick).