OK-
I've been using my new Mr Clean AutoDry car washing system for the past few weeks. I noticed a comment in another NG that it might be possible to use a conventional carwash detergent (rather than the Mr Clean AutoDry detergent) with the Mr Clean deionized water rinse as the final step. I tried it last night with Eagle 1 carwash detergent and it didn't work. The water didn't sheet off like with the Mr Clean detergent. Perhaps it had something to do with the Eagle 1 product, which claims to "enhance waxed finishes".
I now have mild spots on my finish of my 2004 WRX, and the thing didn't completely dry overnight. The water spotting doesn't seem to be too bad - it looks like it'll come off with a proper washing. There's something in their detergent that helps the water come off in sheets. Perhaps there are other detergents that will do the same thing (maybe Meguiar's Soft Wash?). I can't say that you HAVE to use the Mr Clean detergent, but the wrong detergent did lead to a bad result in my case.
Another strange thing is that the unit, and water catridges (incl the refill) are made in China. The trial size detergent is made in Vietnam, although the refills are US made.