Y'know, this actually raised a interesting question of netiquette for me: is the correct response to a line like this (a) leave it as the last word, (b) a one-line acknowledgment, e.g. "Bah-dum-pssh!", or (c) something else entirely?

Incidentally: in a way, you're right, except that professional mathematicians are well-known to say ".999... equals 1". So amateurs should probably treat it the way they treat Gödel's incompleteness theorem (http://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_theorems) - with a humility born of acknowledging the (heh!) incompleteness of their understanding. :D