Just washed mine for the 2nd weekend in a row, thought I'd get away with just sponge and carwash like I used last week but already got a small buildup of black spots in the corners on the 17" alloys that wouldn't budge with my sponge/finger.
First use of my Meguiars All wheel spray and the trusty toothbursh already!
Still hasn't got it all off perfect though...