Have a great time. Be careful, but we felt as safe as anywhere in the US. RENT A BIKE! Riding is AWESOME! While you are in Florence, these guys rent nice road bikes (Bianchi's I think):

http://www.florencebybike.it/

They also speak perfect English, and can give routes and offer suggestions. Getting out of Florence is hectic by bike, but doable.

Also visit the countryside. Cities are nice, but the county and villages are what I miss the most. There are many galleries and things to see in the cities, but I miss the old villages, and people (very weathered and hearty). We saw very few overweight people.

Lastly, rent Under the Tuscan Sun. It has some beautiful shots.