I just came back from a trip to Italy a month ago and based on the advice from a few people here I didn't leave any tip...with one exception. When I went to the Blue Grotto, the guy on the row boat going into the cave kept mentioning that he's providing a special service such as turning around twice inside the cave and taking pictures of us. I knew what he wanted and Rick even warned about it in his book. When we're outside I thought okay, maybe I would give him a 5 Euro tip, but then he said straight to my face "That would be 20 Euros sir!"
I didn't know what to think or say, and was so stunned that I offered no resistance. My wife later said that the people on the boat next to us were also asked the same amount. After I gave him the money, he helped us disembark and said some nice things such as how wonderful he thought our family is etc. Now when I think back about this incident, I wonder what he would have said if I refused to give him the money. Maybe some not very nice things that would have ruined the day for us, in which case I think the money was somewhat well spent.