I think 2-3 weeks before is about right. When I was in college we used to decorate the tree right after Thanksgiving because that was the last time we'd be home together till just before Christmas, but even that felt too soon to me. I hate that Halloween and Christmas merchandise co-exists in stores. I think I'm boycotting Christmas this year and celebrating Yule instead, and making small, meaningful presents for friends and family. I'm going to try to buy absolutely nothing for the season. Ha! Take that you capitalist pigs!