I haven't done this yet, but it sounds great. I have all but the washing soda. I have a friend who just made up a big batch of this laundry detergent and said it works great. I love this tutorial because it has pictures, helpful hints, and short cuts.
If you are trying to do things naturally you may want to look at this post before making the laundry detergent. She has an alternate detergent recipe and other suggestions for natural detergent. The question is is Borax safe to use. I don' have the answer. But if you're using conventional laundry detergent anyway, the first recipe is probably the cheapest and like what you are buying at the store. I have a friend who uses Charlies Soap and loves it! So there you are. Enjoy!
I totally forgot my cousin made laundry soap too. She blogged about it. You can read about it here!