According to someone I know who got a job there, Pisa is a very boring town. Some scenery plus a few tourist traps, low standard of living compared to the US [1], very little to do. Sounds fun before you go, much less fun after you've been there a few months.
Pisa is a nice (but tiny) town, which will be boring if you are young and are use to the big city life. That being said I don't agree that the standard of living is low compared to the US; the standard of living really depends on what you look for.
For me the salary is a poor indicator of quality of life. I'd rather earn less and have more holidays, live in a place with great food, art & culture, slower rhythm of life, less pollution, health care, and nice landscapes.
[1] For hard numbers, I found this site, suggesting a professor in Italy has a real income about 2/3 that of a US professor: http://www.worldsalaries.org/professor.shtml