I stopped doing so for practical reasons.  First, they're heavy and I have arthritis.  Second, I often had to rush off leaving the pans soaking in the sink, not a good thing with cast iron.  Third, other members of the family didn't care for them as I did, requiring frequent re-seasoning.  And last, my kids belonged to the SCA when they were younger and often took the pans on trips, on occasion not getting back home with them.  So, since I am suspicious of aluminum, I use only stainless steel and Teflon lined cookware now.

Never the less, cast iron is a great cooking utensil.  But they do need care.   When you first get your cast iron cookware, wash with hot soapy water and rinse well.  Dry completely.  Apply a thin coat of melted vegetable shortening.  DON'T use butter, margarine or oil which will cause problems.  Coat the entire surface, inside and out.

Place on the upper rack of a 350° preheated oven.  You may wish to place some foil on the lower rack to catch smoky drips.  Bake for one hour.  Turn off oven and wait until the cookware cools.   Scrub with plain hot water and a stiff brush, not using any detergent.  Dry, then lightly coat with vegetable oil to prevent rust.  Wipe with a paper towel and store upside down.

After each use, wash immediately, using as little detergent as possible.  Dry and lightly coat with a little vegetable oil to store.  Many times, for instance when baking corn bread or making pancakes, it isn't even necessary to wash the cast iron.  Simply wipe down thoroughly to  remove any food particles, oil and store.

If someone does let the pan develop rust, it may be necessary to scrub thoroughly with a stainless steel scrubber and detergent, then re-season in the oven as previously described.

Here's some helpful links; as you can see, some instructions differ slightly from the above.  Whatever works for you....

• Lodge Cast Iron  (They also have recipes) 
• Everyday Cook
• Texas Cook
• Epinions