Conan O'Brien is correct. Some words may have ebbed in American usage but that does not diminish the quality of those words. And the nonsense with which they are being replaced? Gadzooks! We do not need strangely compounded words like ginormous (it even looks weird) when we already have gigantic and enormous.
As for thrice, I'm not sure why it has waned. We use once and twice regularly, and the number three is otherwise popular. "Three's a crowd," "third times a charm," and "three strikes and you're out" immediately come to mind. Perhaps the adjective thrice has no colloquialism to keep it in the minds and mouths of the populace.
As Conan has stated, thrice is a perfectly good word and is worth our dedicated attention to restore to its rightful place in our language. For his part, Conan has aired several sketches that present occasions when the word thrice is an appropriate choice. Do your part and use thrice as often as you find occasion to count to three.
Thank the wily crafters at deadcraft.com for the this custom* little Conan you see here. Yet another way to welcome Conan into your home.
*Note: I used the word custom, not custom-made. The adjective custom means made specially for individual customers. (My contribution to the Campaign Against Wasted Words; more to come in future posts.)