For the donut I would use a torus instead of extruding the shape.
For the extrusion they have added "thicken" to the extrude node that will help this a little but you are always going to get oddness in the corners that will need to be manually adjusted even in other apps like max and modo.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 12-09-2011 at 03:04 AM.