Typically we put up the decorations/tree sometime Thanksgiving weekend. Then we take down either January 1st or the first weekend after the 1st depending on how much time we have on the 1st. Lately we've had a New Year's Day dinner at my mom's.
Now, the outside lights usually stay up until the snow melts, but we stop turning them on after January 1st. This year, we have no snow, so they might actually come down w/ the tree. This would be a first.
My MIL- has had her tree up for 13 months now-- yep-- they put it up in November of last year (2005) and still haven't taken it down. That goes for the tree, the garland, and all the indoors decorations. She was of the mindset her boyfriend put it up, he can take it down. My dh says if someone doesn't take it down by Easter this year-- he's saying something.