I have to agree with Chris on the cheesiness of singing carols. I had the same kneejerk reaction when I read Carol's post. All I could think of was that if it had happened, I'd have been cringing on the sofa and would have had to turn the sound off.
I don't think Christmas caroling in and of itself is cheesy--but some situations in which people might burst with carols coming out of their mouths really ARE.
For instance, I have no problem walking around a nursing home (or a friend's neighborhood) with a group of people--be they friends or people from church, or just a group of family members--singing Christmas carols. I also have no problem singing them with family on a quiet Christmas Even night.
But having Lois and Sam burst into song at the end of HIWTHI, just as a plot device? Definitely cheesy.