We heard that the state museums (The Uffizi, The Accademia, The Pitti Palace, etc.) were free this Sunday, the 18th (tomorrow) - but I have not been able to find anything about it on the web anywhere. The Italian/Florentine museum websites are pretty notorious for not being up to date unfortunately. We are going to go over to San Marco Sunday anyway to see if it is true.

Update: There is also a Carnevale parade on Sunday starting at 2:00 PM - last year it went from Piazza Ognissanti to Piazza Signoria, the route is probably similar this year. Phone 055 276 8030.