In my spark layout updateDisplayList method (not complete, just the relevant stuff):

var totalAngleSoFar:Number = 0;
            totalAngleSoFar -= Math.PI / 4;

            iter.reset();
            while (element = iter.nextElement())
            {
                polarElement = IPolarElement(element);
                var position:Point = RadialUtil.convertPolarToCartesian(new Point(polarElement.radius + layoutTarget.itemOffset, totalAngleSoFar), polarElement.origin);
                var targetRotation:Number = RadialUtil.convertRadiansToDegrees(totalAngleSoFar);


// If I comment this out, all is well but everything is rendered straight. The x, y seem to be correct, though:
                                polarElement.rotation = targetRotation;


                element.setLayoutBoundsPosition(position.x, position.y);



                // Move on to next item
                totalAngleSoFar += polarElement.theta;
            }

RadialUtil:

package net.skai.utils
{
    import flash.geom.Point;

    public class RadialUtil
    {

        // in Polar points, x == radius and y == theta.

        public static function convertCartesianToPolar(input:Point):Point {
            var theta:Number;

            if (input.x > 0) {
                theta = Math.atan(input.y / input.x);
            } else if (input.x < 0 && input.y >= 0) {
                theta = Math.atan(input.y / input.x) + Math.PI;
            } else if (input.x < 0 && input.y < 0) {
                theta = Math.atan(input.y / input.x) - Math.PI;
            } else if (input.x == 0 && input.y > 0) {
                theta = Math.PI / 2;
            } else if (input.x == 0 && input.y < 0) {
                theta = Math.PI / -2;
            } else if (input.x == 0 && input.y == 0) {
                theta = 0;
            }

            return new Point(Math.sqrt(input.x ^ 2 + input.y ^ 2), theta);
        }

        public static function convertPolarToCartesian(input:Point, origin:Point = null):Point {

            var retVal:Point = new Point((input.x * Math.cos(input.y)), (input.x * Math.sin(input.y)));

            if (origin) {
                retVal.x += origin.x;
                retVal.y += origin.y;
            }


            return retVal;
        }

        public static function convertDegreesToRadians(input:Number):Number {
            return (input * Math.PI) / 180;
        }

        public static function convertRadiansToDegrees(input:Number):Number {
            return (input * 180) / Math.PI;
        }
    }
}