eh, people are nice in rome. it's obivously the city with the most tourists, and it's always really easy to spot the americans...it's sad, but you just look for people who are overweight and/or wearing jeans.
in rome, eat at tre scalini. and piazza navona is a fun little lively spot. lots of people and art on the streets and a bunch of places to eat. behind it, the corso rinascimento is a neat area with lots of shops. there's a swell little shop that sells all kinds of different things made by all of the monks in the region.
from rome to florence (are you going by the rail?) you can either go up the left and cut over at pisa, or go up the middle. i'd go left, as i loved pisa and there are alot of towns on the water. the middle is cool too though, my parents are in perugia (a few hours outside of rome) and it's gorgeous.
in florence, if you can stay at the savoy, it will become one your top ten lifelong memories. regardless, visit the piazza della republica and eat at gilli. say hi to the manager, and ask him to tell you about his hometown, lucca. you could spend a whole day at the uffizi...don't get the headsets though, or it will take up your whole trip. and i'll reserve my really rude comment here, but let's just say that you'll be swamped by particular people with cameras if you go on the weekend.
just my suggestions. have fun.