About how all you ever have to do to clean them is wipe them out, and also about how they're impossible to clean? Let's set the record straight.
For When Your Pan is Already Pretty Clean
Sometimes, you will cook things (like pancakes, say) that honestly do not require anything more in the way of clean-up than a wipe-out. Rub the cook surface with a dry cloth, and you're good. It does happen. Even if a tiny bit of debris is left, sometimes the cloth is enough to handle this all by itself.
Maybe you want to sprinkle a bit of salt in there and then wipe. A little friction to dislodge the sticky: another fine method.
But sometimes, the need will be greater.
For When You've Created a Cruddy Mess
Sometimes, your buffalo-and-rubbed-sage hamburger patty will have glued a fatty gunk to the bottom of the pan. Your scrambled eggs will have left a crusty layer. Do not despair.
1. Hit it with water (that's right) and scrub that thing out with a metal scrubber.
Use a steel or copper scrubber. You don't have to use soap — it doesn't add anything to the process. Just a plain, soap-free, metal scrubber will take care of everything.
2. Set the wet pan on the burner, medium-low, and wipe it with a dry cloth as it warms.
Watch the heat evaporate every last trace of moisture. Kinda neat. Also important for preventing rust.
3. Add some fat.
Flaxseed if you like, but butter or other kinds of fat are okay. These won't polymerize like flaxseed oil, but they will contribute something to your seasoning, and they'll protect your pan from moisture and rust. Wait till the fat is pretty hot, and then ...
4. Rub it into the bottom and sides of your pan with the dry cloth.
Your pan is now glossy, rust-free and re-seasoned. And all it took was about 30 seconds. Seriously, cleaning cast iron is way easier than scrubbing out a dirty stock pot.
For When Apocalypse has Happened in Your Pan
So let's say you try the above, and after about two seconds of scrubbing you're like, "Man, this is harder than I want it to be." There is another way.
1. Pour some water into the base of the pan, just enough to cover it.
2. Put the pan on the burner, on high.
3. As soon as it starts to simmer, scrape the cook surface with your flat, metal spatula. The crud will peel up off the bottom like a dream.
4. When you've got most of it loose, rinse the pan under the faucet again and get every last bit off with the metal scrubber.
5. Then, steps 2-4 from "When You've Created a Cruddy Mess," above.
Note, this method is more stressful for your pan. It will wear away a few of your nonstick layers. So use it sparingly, and take a bit of care afterward to rebuild.
What if your pan retained moisture somehow, and now it's rusty?
Hit it with water, scrub away the rust with your metal scrubber, and add a new layer of fat (steps 2 through 4 again).
What if you cooked something really acidic, like tomato sauce, and you lost some layers of seasoning?
Then add some more seasoning.
What if you cooked something like a white sauce, and it's not exactly stuck to the pan, but it's too gooey to wipe out?
Water. Scrubber. Heat. Fat. Cloth. (If it's turned to glue, use the "Apocalypse" instructions above.)
Is there anything I should never, ever do to cast iron?
Sure. I mean, don't put it through the dishwasher. And don't leave it on the burner for long enough that the heat breaks down all those layers of polymerized fat, thereby un-seasoning your pan.
While we're at it, don't set it on the burner, squirt in some oil and walk away thinking, "I'll just let it warm up a little," only to forget about it, returning several minutes later to find that you've just seasoned yourself a big, uneven, polymerized puddle-sculpture in the center of the pan. (I have never done that.)
Point being, yes, there are things you shouldn't do to your pan. On the other hand, mistakes are okay. Pretty much anything you do, you can undo in time, by following the instructions in this post and the one before it.
There is only one surefire way that I know of to ruin your pan, which you should never do. Never let it sit on the heating element dry (without any food or fat in it) for long enough that the pan cracks.
And That's About It
Once you get comfortable with these two processes (cleaning your pan and re-seasoning it afterward), you may find yourself cooking with it every time you cook. I mean, it's non-stick, it'll never wear out (ever), it will never flake weird stuff into your food, it's easy to clean, it adds iron to your diet, and the thermal mass of the pan can be really useful depending on what you're cooking. I love cast iron. What's the downside again?