During our time in Florence, we took an overnight trip to Pisa.
Here's the thing, there is nothing to do in Pisa besides see the tower. In short, only visit Pisa for a a quick day trip — don't go out of your way for it.
Although we had planned an entire day and night in the city, it did not go completely to waste. After having camped for two days, it was wonderful to have a warm shower and blow dried hair. I can't begin to tell you how much I appreciate a shower and clean, straight hair.
Our initial plan was to visit the beach while in Pisa, but we could not find the bus we needed and a shower was calling our names. We listened and headed back to the hostel to nap, eat, shower, and watch the Olympics (which was going on while we were in Europe). Who knew that the nicest hostel we would stay at would be in Pisa?