I know that some schools (such as NYMC) are offering interviews on December 22nd/23rd, so it is conceivable that their admissions offices will be open that day and that they might be processing applications/sending out news.
This is just speculation, however, so take it with a grain of salt and stick with your assumption to be on the safe side.
I think I become more neurotic everytime there is a break. Knowing that my application is lying somewhere in a dark cubicle gathering dust instead of being reviewed by some adcom member is enough to drive me bonkers!
I'm waiting until January. My fear is that some mail worker will drop them off into a giant pile of update letters, they will fall in a crack between the desk and the wall, and will never be read. Or if I send it in email, then it will take the person 2 weeks just to get through their inbox.