Rectangles without arcWidth/arcHeight and without rotate/shear shouldn't use AA regardless of the hint setting. Fairly simple painting time optimization. Most applications make heavy use of rectangles (though many of them also use rounded rects which won't benefit from this optimization). Some like "BrickBreaker" have 2500 such rectangles, and it would be nice if in that case they didn't have to get poor performance without manually setting those bricks to smooth:false.