This article courtesy of www.arttrav.com:
Big Florence news: From Sunday October 25th 2009, Florence’s landmark Piazza Duomo is going to be pedestrian only. This means a total stop to cars, busses, motorini, bikes, and taxis going past the duomo
For tourists, this means no more backing up against chains as you try to get that perfect photo of the facade; think of the new photographic opportunities when you can stand in what used to be the middle of street!
For residents of Florence there will be some new inconveniences. Many busses will be rerouted at Piazza San Marco to Santa Maria Novella 
Station, so the center will be less accessible. The mayor’s office announced that this should be resolved soon by new electric bus routes. You can download the new bus route explanation here.
These Festivities are scheduled for the Sunday October 25 launch:
1) The mayor’s office has announced that there will be festivities for the launch of the pedestrian only piazza; these will be announced on the website www.unbacioneafirenze.net .
2) Residents of Florence and anyone born in Florence can get into Palazzo Vecchio for FREE that day, and will be able to visit normally closed areas.
Hooray for piazza Duomo!!! See you at the festivities.