Wow, this is complicated:
It works, except for things which don't have drivers yet. Strangely, in conventional speech, things without drivers don't work, but the OS as a whole is considered to work if it runs and is usable.

At the moment, sound is missing drivers, and some other things may be as well. (I'm not running it, so not sure.)

Since you asked specifically about cupcake, it seemed reasonable to suppose you knew about the state before Google pushed cupcake out, and wanted to know if the update had broken anything; it hasn't.