UPDATE: June 2012- I used this for quite some time and began noticing a film being left on my dishes. I started alternating this homemade version with a store-bought gel pac detergent every 2 or 3 loads and that has helped a lot. Also, you might notice that after a few days in the airtight container, your detergent might harden up a bit. I just used a fork to break it up and continued using it from there.
Homemade Dishwasher Detergent
1 cup of Borax
1 cup of Super Washing Soda (Or baking soda)
1/2 cup Kosher salt
15 packets of unsweetened Lemonade flavored Kool-aid (or 1/2 cup citric acid)
Mix the ingredients together in a dry container with a lid. Use 1 tablespoon for each load and they also recommend adding vinegar to your rinse agent dispenser for an even better cleaning. But, in all honesty, I didn't think I would like this. I use Cascade gel and I love it. My dishes always came out pretty clean and I didn't have much hope for this powdered detergent...BUT...my dishes have NEVER looked this good straight out of the washer. My jaw dropped, there was a huge difference in my crystal and silver. This stuff works and since you already have the ingredients from making your own laundry detergent, I say, give it a try!