In the first year, when MOOL was daily, I had a holiday-themed episode around December. It was fun, and I don't mind them as long as they match up with my time table on where the series is. While I agree that it makes the series more intimate to match up holiday goodness as it corresponds to our witnessing of them in the real world, it should exist to further story and conflict. Doing the episode every year just to settle a proverbial checklist does not always result in a meaningful holiday episode, especially when it depicts an inaccurate picture of how things really exist and disrupts the plot. I think you can incorporate it in big ways, like Dallas indicated with some of his samples, or just by having characters consciously aware that the time in which the events in their lives happen to be transpiring is around thanksgiving or st. patrick's day. As long as it entertains and furthers story, it should not be a problem.
