I've gone through several bottles of QEW, and it's a wonderful product. However, its competitor - Optimum No Rinse - is better IMO. The best way to wash a car is to use a regular hose/bucket method, but these products are a great alternative for those who do not have access to one or want to stay in the garage during long winters.
I use this method with good success:
- Fill up 2 buckets of water with 5 generous capfuls of ONR with 5 squirts of any quick detailer
- Use 1 quality microfiber towel in each bucket as my wash towel
- Fill up a squirt bottle with 2 generous capfuls of ONR and a couple squirts of QD to prime the surface
- Soak the towels in the bucket, and fold into 1/4s
- Use one side of the towel going in a linear direction, and fold again on a clean side
- After every side is used, wash the towel in the bucket
- I like to divide the car into panels to wash (4 sections of the hood, 1/2 the roof, half a door, etc)
- After each section, use a waffle weave microfiber towel to dab the surface (don't wipe!) to get rid of the water
I've used wash mitts before, but I find using a microfiber towels yields for better results with minimal marring. The wash solution itself is pretty potent stuff, so a little definitely goes a long way. I used to follow the directions on the bottle, but I just eyeball it nowadays.
Some people swear that using QEW or ONR won't marr the surface, but I think that it has to do more with technique rather than the product itself. As long as you're good about using clean towels, don't apply too much pressure, and take your time you'll minimze the chances of scratching the paint. Feel free to change out the buckets if they get dirty or even use fresh towels if they get stained.
Using a spray bottle to prime the surface helps to dislodge sediments on the paint which allows for the wash towel to pick it up easier thus reducing the chance of marring the paint. For dusty cars this really isn't necessary, but it's more useful for really dirty ones. Also the quick detailer acts as a lubricant which helps reduce marring - I definitely noticed a difference when not adding a QD and when adding a QD.
I've been using QEW and ONR for the past couple years, and it's definitely made my life a lot easier. I can go do the entire car with washing and drying in about 15-20 minutes now, but it does take practice to go quickly. You can also use the spray bottle solution as a wheel and window cleaner as well - it's pretty versatile. My neighbors were anal about me using the common grounds hose (I live in a townhouse with a HO Assoc), so the ability to wash in the privacy and comfort of my garage is really nice.
There's a lot more I could add, but feel free to ask any questions