I pretty much do cardio all the time, whether cutting or bulking. However, I NEVER do it on the same day as I weight train. One big plus since I started HST, is it works perfectly for the way I like to train. I'm doing HST 3 days per week, Monday, Wednesday and Friday, and fit cardio in on Tuesday, Thursday and Saturday. (Usually incline walking on a treadmill, or interval type stuff on an eliptical machine, but never more than 30 minutes of either).
I generally keep my food intake exactly the same whether it be a cardio or weight day, and I've found I seem to be able to maintain BF levels fairly well, and keep the muscle gain going. If I feel I'm leaning out a bit too much, I'll drop the Saturday cardio, and just do two days a week.