I visited this place three times. First one in my first international trip, in 1987, second time with my wife in 1998, and third time in July 2012 with my family and friends. All three times I had the same impact when entered the Piazza and walked towards its center: my heartbeat got crazy, I got very close to crying, and finally, when sat down in the floor in the center of the Piazza, it was pure peace, like we are not in the middle of the crowd, but instead in the middle of a desert field. Impressive. And when the sun goes down behind the buildings, it is amazing and unforgettable.
Don't forget going upstairs to the top of the tower. It is messy, hard, but worthwhile.

The piazza was huge and it was a good time to visit as there weren't too many tourists. After a few hours touring the city, we were able to appreciate the piazza more while relaxing and sipping coffee at one of the many cafe's around the piazza. Nice place to just sit and relax while enjoying the view of the square and do some people watching.

a small pearl of italian architecture. seen several times on tv, pictures and cinema you cannot realize how beautiful it is till you walk down the streets and you enjoy the view of this beautiful square.

We visited in winter and it was raining so the entire town was quiet with little people and tourist. The square was pretty much vacant so gave you the chance to look around without people getting in your way. Still few to many pigeons around though. I imagine the cafes and restaurants on the square would be expensive like most other European places. You can't miss seeing it if you are in town.