I was amused, because they only sang one traditional carol, and the rest was a medley of modern ones, fashioned after ABBA songs! Yes, I remember there was Mamma Mia and Super Trooper (?) as well as that song made famous in Sister Act.
I like traditional carols and songs, my firm favourites being O Holy Night and Winter Wonderland, and Have Yourself a Merry Little Christmas. This last one was performed by Colbie and Jason last night on Letterman :)
By the way, Last Christmas by Wham does not count as an Xmas song.