Dec 1st and we take them down Jan 7th.
I always want to put them up in November but I'm never organized enough to get around to it, so I keep them up past New Year's.
Last year I kep them up for months and months, on purpose. I had a really tough year and I'm a total Xmas junkie so I was like, "I'm going to treat myself to Xmas all year long" LOL
I put mine up the day after thanksgiving and usually take them down shortly after new year.