I don't do it, because I am actively trying to avoid making emotional connections with food. Food should be about fuel, mostly. I don't want her to make the mistakes I did, and see food as an emotional crutch. I don't want her to be feeling miserable, and hoping to feel better and automatically going, "Well, hey, remember all those awesome times you had? Your birthday, whenever you were good, when you did well on your report card, etc etc... they all involved cake/pasta/whatever else! Go on... go make that happen!"
So, no. I don't. When we have junk, it's sporadic. Apart from birthday cake... but I don't think I can take away that and not be a jerk. But generally, if we have junk it's because I'm being lazy... she doesn't get food rewards.