I have always been a fan of the two bucket suds and hose method for years, and kept my car relatively swirl-free... when I moved to the 328i, I tried a new method. I had my car Opticoated locally for a good price and now I wash with Optimum No-rinse. Originally stuck with the 2 bucket method still but I came across this:
and have been doing it in my garage with just a bucket of water and some microfiber towels. I have to say, it's amazing - quick and easy, stay warm inside, no swirl marks, FAST, and easy cleanup...
I'll keep this thread updated in the future if I run into any issues but so far after 3-4 washes all has been great.
As for the opti-coat - Not sure how well it works, but I have no swirls after 6k miles and its either the coat or the wash method that has been helping. The car also looks nice and waxy right after a wash.