Yeah, I've tried mixing cider with various things, and it just doesn't go with coffee or chocolate - anything bittersweet brings out the unpleasant woody bitterness of apple, while the fruity sweetness and acidity of the apple juice doesn't necessarily play well with the subtler flavors of other things.

We didn't end up making the eggnog, but we had scrambled eggs instead, and I made mulled cider a couple of times. ... Also ... I put Bailey's in my coffee when we ran out of milk the other day. *grins* That was tasty.