I would NEVER use anything with bristles on your paint!!!!!
I use the natural fibered 'wooly mitt'. I have seen several places HIGHLY reccommend this, since this really WILL get the dirt away from the finish.
In fact, I use two. One is only for the dirt that flies up because of the lack of mudflaps. Once I get that dirt off, I use another for the rest of the car.
ONLY use natural fibers on your car, unless it is a microfiber cloth.
<span style='font-size:12pt;line-height:100%'><span style='color:blue'>I don't drive fast,</span> <span style='color:red'>I FLY LOW</span></span>