I went here tonight with a group of friends, and the food was fantastic.
Many of the restaurants in Pisa seem to serve not-so-great food for tourists, but La Cereria serves high quality fresh food with fantastic ingredients.
We started with a large family style bowl of linguine vegetariane, which was linguine with vegetables, garlic, and olive oil. The pasta was perfectly al dente, and the veggies included radicchio, artichokes, kalamata olives, mushrooms, zucchini, and tomatoes. All of the veggies were fresh and delicious.
Next I had a mixed salad, made up of arugula, radicchio, roasted corn, carrots, and tomatoes. Again, the ingredients were fresh and delicious.
Finally, we shared a pizza vegetariano without cheese. The pizza had a wonderfully thin crust, and the sauce was fresh and full of tomato flavor.
This was my best meal in Italy so far, and if I have a chance, I'd love to go back again.
The only reason I'm not giving them five stars is that their vegan choices were fairly minimal. That's not unusual from what I've seen so far, but it's still a bit disappointing. In particular, none of their antipasti were vegan.