I learned just in the nick of time that Florence stores have huge end-of-season sales during the second week of January. This year they started the Saturday after Three Kings Day (January 7th) - I saw the date posted in the paper (but I would assume it's the same general schedule every year). On Saturday the streets were mobbed - I've never seen Centro so jammed with people. Sunday many of the stores were still open and they seemed much less crowded.
Everything is on sale, with discounts of about 30-60% -- so if you have your eye on something special, it's probably worth waiting for these sales. I picked up an 80 euro sweater at Stefanel for about 50 euros. Stefanel also had a winter jacket at 50% off, but they didn't have my size. Finally, I found a pair of winter boots (which I desperately needed since it's been so wet and cold this winter!), they were originally 150 euros down to 109. I saw other great deals at Benetton, Sisley, Zara, Coin (department store) and Prenatal (for the kids). Every store I walk by has huge "SALDI" signs. It's tempting to check out every one, but I think I've already blown my budget!