In live home tourney play, I usually like to say to my opponent something like, "Well, I'd wish you luck, but the way you usually suck out on the river, I'm just hoping you miss for once". Or sometimes, "We're both all in, God I hope you miss." Or finally, "Good Luck..to me, I want to knock you out (or double up through you)." In any case, I usually say it with a great deal of charm, so that works for them.
But seriously, I never wish an opponent good luck when I'm in a hand with them. Additionally, if I'm not in the hand, I will usually wish good luck to the person with the larger stack because if they win one more person goes away.
This may all sound a little callous, but poker is war. There are no friends on the felt battle field and I'm not one to put on a phony facade for the sake of pseudo sportsmanship. But again, that's me. I've seen plenty of others be kinder and gentler, but it doesn't suit me. And for the record, the more callous statements above don't come out immediately, they come out when appropriate later once they are deserved.
Guess that is my long winded way (like usual) of saying I like John's post.