I'm bad at recalling more than a few lines of songs (or anything of any length) verbatim on my own, but I like that this stuff is such a part of me that I'll sing along without even realizing it.
Edit: I am thus particularly thrown when the next song is in French and I am totally at a loss.
Also, I am such a traditionalist. Every time I listen to this "O Come All Ye Faithful" I think that (1) it should be "yea [Lord we greet Thee]" (pronounced "yay") instead of "yes" and that (2) "[Jesus to Thee be all glory] giv'n" should not be two syllables. [I am incredibly impressed by his "Lord" in that last line, though. I can manage to do the "Gloria" in "Angels We Have Heard on High" all in one breath (practice from church), but singing along to this CD I can sing along with him through that entire "Lord" just barely, and any quality of voice gives out well before he finishes; he's got this remarkably strong almost operatic (?) voice going on the end of this song.]