I've made a model just for fun, with perfect smooth corners all around. So smooth in fact that in hidden line and wireframe mode you absolutely only see the outline (cellshade-ish).
Just made it for the kicks, perhaps the way I made it would help someone. Keep in mind all corners can be perfect - just offset the lines you want to round the angle from, and draw a circle from where they cross. Then trim, delete temporary lines and you're done.