What is the danger in cross contamination?

Whilst you'll probably be fine using the same knife and chopping board to prepare everything that's going in an "all in one" meal such as a stew, here's the reasons I have for never doing so:

• It's a bad habit to get into. It's very easy to slip-up and forget that you're not making an "all in one" meal and thus chop some lettuce on a board you've already used for slicing raw bacon when making a salad, if most of the meals you make are "all in one" and you usually don't have to "worry" about cross-contamination
• It doesn't take that long. Washing your chopping board down with hot soapy water and a clean sponge/scourer takes literally a few minutes, the same can be said for a knife. If you're pressed for time you could turn the board over and use a fresh knife. That assumes that the work surface was clean beforehand and the food being prepared on the "first" side was dry and thus won't have liquid run-off that's contaminated the underside of the board
• It's not worth getting wrong. If you make a mistake and get food poisoning, or worse - give someone else food poisoning, you'll really wish you'd done your utmost to prevent cross-contamination.

Cross contamination isn't a problem for food that is going to reach high temperatures, it's a problem for things that won't. Uncooked veggies, serving dishes, already cooked bread, handles of utensils you will continue to touch through the whole cooking process, etc.

If you want to save yourself one extra wash, cut the bacteria friendly food (like meat) last. Be sure to wash the board after cutting the meat, wipe down the counter any juices may have touched, and wash your hands before touching the next food or utensil.

As Rob eluded to, while the dangers of cross-contamination vary in each cooking scenario, developing good habits and a hightened awareness about food safety will help decrease the possibility of contracting a foodborne illness.

Cross-contamination is a very real danger, especially when handling meats that are sitting out in the 40F-140F temperature range, where bacteria growth increases. Being conscious of everything that touches raw meat will help to avoid this danger. While all of the food might go into the same dish and be cooked at a high temperature, your tools aren't cooked with the food; this includes your hands, knives, boards, spoons, and anything else that you use to touch the food throughout the cooking process.

For example, when I'm preparing something on the grill, I'll generally try to cut any vegetables first, followed by the meat. Since my hands come in contact with the raw meat, I make sure to wash them with hot soapy water after working with the meat. I'll usually use a tool of some sort to help get the meat on the grill and to flip it. If the tool was used to handle raw meat at the beginning, I'll wash the tool before using it to take the cooked meat off of the grill. While I'm not sure exactly how much I am exposed to the dangers of cross-contamination at each step in the process, my heightened consciousness and cleaning habits help to decrease the chances that I (or my dinner patrons!) will contract a foodborne illness.