What do I have to worry about when using a cast iron skillet as opposed to nonstick?
Arm fatigue.

They're heavy enough that you'll need to consider how you hold them as you're dumping food out of them.  You'll often see chefs on cooking shows grabbing the handle in a strange way, where the grip is from underneath, and then they hold it with the handle at the top and the pan almost dangling below.

Learn this technique, and you won't end up straining your wrist from trying to hold the pan out in front of you as you scrape the food into a serving dish.

... Also in a similar fashion -- if you're used to being able to flip your food without needing a utensil ... it might take a little bit of strength training before you're ready to do that with cast iron.