Mosca,
It depends on what your are trying to accomplish. Dawn (or any other dish detergent) will not take off a sealant that's been applied recently. Sealants are made to bond very strong to the paint so a simple dish detergent wash will not strip it effectively. A fresh coat of wax properly applied may even take 2 or 3 washes to get rid of the wax completely. Washing with a dish detergent to remove sap will still take some effort. However, if you simply want to remove some loose wax etc, then it will work. Sal from Zaino recommends it as a FINAL step before the sealant (after you have completely prepped your car as a final step to ensure most of the oils are removed).
If you're looking for something to start with your prep rather a final step in preparation. Prep-sol or a APC+ diluted to the proper concentration is probably best.
If you're looking for something to remove polish fillers during swirl removal, I'd suggest an 50/50 IPA/Water spritz or a APC+ diluted to 1/3 or 1/2 of what is required for wax removal.
As a note: Dawn may not even be the most effective dish detergent. It's gotten soo much hype partially due to Sal's recommendation. Ivory / Sunlight may be even more effective than Dawn. Basically, any dish detergent without moisturizers, added perfumes (florals etc.) will work just as well. Granted, Blue Dawn is pretty inexpensive.
I myself, won't use dish detergent on my car any longer. I have used in the past but I just don't see that it does that much more cleaning that regular car wash to justify it's use (which could potentially damage the clear if you use it to repeatedly). For Autopians, it's most likely a none issue. But for the everyday Joe, it's definitely an issue if they don't understand the proper use of a dish detergent.
Paco