I brew a lot, about 4 years experience and from what JZ says, use good sanitation practices, maybe separate racking tubing and you shouldn't have a problem. When you think about how much bacteria and yeast is coating everything, you're really not changing the equation that much. I feel the biggest source of cross-contamination would come from handling successively. I use a covered container of prepared sanitizer (star-san) dip my hands and wait one minute before handling the sensitive items. From what I've read most problems brewers have come from milling grain too close to fermentation and racking areas.
Mark