In South Philadelphia, windows decorated for Christmas have come to resemble elaborate stage productions, most of which have already been taken down. Those that are remaining will nearly all be gone after today, which is the traditional feast of the Epiphany. We are asked to keep physical reminders of Christmas around until at least January 10th, the Feast of the Baptism of the Lord. Years ago, it was traditional to keep the creche up until the Feast of the Presentation on February 2nd
I don't ever recall a church keeping the creche up until then but I'm told this is commonplace in Italy, to the point where there were only a few days between Candlemas and Ash Wednesday (the year Easter fell exceptionally early).
Aside from the cheer that keeping the lights and the tree around for a little bit longer provide, I like the idea of keeping my Nativity scene and candles in the front window until Candlemas for the opening it provides with my neighbors, who will often remark that I "still have my decorations up." It's a simple way of giving public witness to our faith.