i find that it's hard to get the brush to move back and forth without flipping around wildly, it doesn't need to flip 180 degrees to paint backwards, 0 degrees works just as well. if you've used inkscape (and if you haven't give it a try and use the caligraphy brush and play with it's parameters to see what i'm getting at), obviously it doesn't need to be as dramatic as that unless you're doing calligraphy style strokes (although that'd be a nice artrage feature) but with the brush flipping around like crazy it can be hard to do some neat strokes