I've also discovered....by accidentally spilling some while making it once :)...that it cleans carpets and countertops too!!! So, since then, I have used it on tough carpet stains...as a stain pre-treater on clothing...to take out stains on my car's cloth seats....to clean stains on my son's carseat....to clean stains on the couch...the possibilities are endless with this stuff!!!!
Ingredients:
1/3 bar of Fels-Naptha soap
1 cup Arm & Hammer washing soda
1 cup 20 Mule Team Borax
water
You will also need a very large pot or bucket (I use a 2 gallon cooking pot)

*Note...If you notice the size of these packages compared to the amount you use in the ingredients, then you'll realize that these things will last you for a while throughout multiple times of making the detergent...which equals lots of money saved. I pay approximately $4.00 for the box of Borax, $4.00 for the box of Washing Soda and $1.00 for the Fels-Naptha. When you figure the minimal amount of these things that goes into the detergent, the cost of a gallon of this homemade detergent is nearly just $1.00!!! Now that's cheap!!!
Directions:
Grate the Fels-Naptha soap with a cheese grater and put into a large pot (if you don't have a large pot, just use a small one and then transfer into a bucket for mixing after heating). Add 6 cups of water and heat until the soap melts. Add washing soda and borax and stir until both are dissolved. Remove from heat. Pour 4 cups of hot water (or pour these 4 cups into a bucket, then add your soap mixture to it) and stir. After that, add 1 gallon of water, along with 6 cups of HOT water and stir. Let sit for about 24 hours and it will "gel". Once it is done sitting, I pour it into old laundry detergent jugs that I have saved. (but you could put it into any container of your choice)
I use about 1/2 cup to 1 cup per load of laundry. You have to shake up the bottle before you use the soap each time because it tends to settle. Also, it isn't really a "sudsy detergent, so don't be alarmed if you don't see suds in the water when you add it.
*If you prefer to use powdered detergent over liquid, you can use the above ingredients minus the water. However, please realize that if you wash your clothes in cold water to conserve energy, the powder tends to cake up and not dissolve well.
*If you have trouble finding these products at your store of choice, I've found that Kroger's carries all of these products.